WorldWideScience

Sample records for surfaces including electron

  1. Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion

    Science.gov (United States)

    Scholz, Robert; Floß, Gereon; Saalfrank, Peter; Füchsel, Gernot; Lončarić, Ivor; Juaristi, J. I.

    2016-10-01

    A Langevin model accounting for all six molecular degrees of freedom is applied to femtosecond-laser induced, hot-electron driven dynamics of Ru(0001)(2 ×2 ):CO. In our molecular dynamics with electronic friction approach, a recently developed potential energy surface based on gradient-corrected density functional theory accounting for van der Waals interactions is adopted. Electronic friction due to the coupling of molecular degrees of freedom to electron-hole pairs in the metal are included via a local density friction approximation, and surface phonons by a generalized Langevin oscillator model. The action of ultrashort laser pulses enters through a substrate-mediated, hot-electron mechanism via a time-dependent electronic temperature (derived from a two-temperature model), causing random forces acting on the molecule. The model is applied to laser induced lateral diffusion of CO on the surface, "hot adsorbate" formation, and laser induced desorption. Reaction probabilities are strongly enhanced compared to purely thermal processes, both for diffusion and desorption. Reaction yields depend in a characteristic (nonlinear) fashion on the applied laser fluence, as well as branching ratios for various reaction channels. Computed two-pulse correlation traces for desorption and other indicators suggest that aside from electron-hole pairs, phonons play a non-negligible role for laser induced dynamics in this system, acting on a surprisingly short time scale. Our simulations on precomputed potentials allow for good statistics and the treatment of long-time dynamics (300 ps), giving insight into this system which hitherto has not been reached. We find generally good agreement with experimental data where available and make predictions in addition. A recently proposed laser induced population of physisorbed precursor states could not be observed with the present low-coverage model.

  2. Conversion electron surface imaging

    CERN Document Server

    Irwin, G M; Wehner, A

    1999-01-01

    A method of imaging the Moessbauer absorption over the surface of a sample based on counting conversion electrons emitted from the surface following resonant absorption of gamma radiation is described. This Conversion Electron Surface Imaging (CESI) method is somewhat analogous to Magnetic Resonance Imaging (MRI), particularly chemical shift imaging, and similar tomographic reconstruction techniques are involved in extracting the image. The theory behind the technique and a prototype device is described, as well as the results of proof-of-principle experiments which demonstrate the function of the device. Eventually this same prototype device will be part of a system to determine the spatial variation of the Moessbauer spectrum over the surface of a sample. Applications include imaging of variations of surface properties of steels and other iron containing alloys, as well as other surfaces over which sup 5 sup 7 Fe has been deposited.

  3. Good Security Practices for Electronic Commerce, Including Electronic Data Interchange

    Science.gov (United States)

    1993-12-01

    FROM - TO) xx-xx-2002 to xx-xx-2002 4. TITLE AND SUBTITLE Good Security Practices for Electronic Commerce , Including Electronic Data Interchange...Report 12/1/1993 4. TITLE AND SUBTITLE Good Security Practices for Electronic Commerce , Including Electronic Data Interchange 5. FUNDING NUMBERS 6...Maximum 200 Words) Electronic commerce (EC) is the use of documents in electronic form, rather than paper, for carrying out functions of business or

  4. Two-fluid turbulence including electron inertia

    Energy Technology Data Exchange (ETDEWEB)

    Andrés, Nahuel, E-mail: nandres@iafe.uba.ar; Gómez, Daniel [Instituto de Astronomía y Física del Espacio, CC. 67, suc. 28, 1428 Buenos Aires (Argentina); Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón I, 1428 Buenos Aires (Argentina); Gonzalez, Carlos; Martin, Luis; Dmitruk, Pablo [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, 1428 Buenos Aires (Argentina)

    2014-12-15

    We present a full two-fluid magnetohydrodynamic (MHD) description for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure, and electron inertia. According to this description, each plasma species introduces a new spatial scale: the ion inertial length λ{sub i} and the electron inertial length λ{sub e}, which are not present in the traditional MHD description. In the present paper, we seek for possible changes in the energy power spectrum in fully developed turbulent regimes, using numerical simulations of the two-fluid equations in two-and-a-half dimensions. We have been able to reproduce different scaling laws in different spectral ranges, as it has been observed in the solar wind for the magnetic energy spectrum. At the smallest wavenumbers where plain MHD is valid, we obtain an inertial range following a Kolmogorov k{sup −5∕3} law. For intermediate wavenumbers such that λ{sub i}{sup −1}≪k≪λ{sub e}{sup −1}, the spectrum is modified to a k{sup −7∕3} power-law, as has also been obtained for Hall-MHD neglecting electron inertia terms. When electron inertia is retained, a new spectral region given by k>λ{sub e}{sup −1} arises. The power spectrum for magnetic energy in this region is given by a k{sup −11∕3} power law. Finally, when the terms of electron inertia are retained, we study the self-consistent electric field. Our results are discussed and compared with those obtained in the solar wind observations and previous simulations.

  5. Appendage mountable electronic devices conformable to surfaces

    Science.gov (United States)

    Rogers, John; Ying, Ming; Bonifas, Andrew; Lu, Nanshu

    2017-01-24

    Disclosed are appendage mountable electronic systems and related methods for covering and conforming to an appendage surface. A flexible or stretchable substrate has an inner surface for receiving an appendage, including an appendage having a curved surface, and an opposed outer surface that is accessible to external surfaces. A stretchable or flexible electronic device is supported by the substrate inner and/or outer surface, depending on the application of interest. The electronic device in combination with the substrate provides a net bending stiffness to facilitate conformal contact between the inner surface and a surface of the appendage provided within the enclosure. In an aspect, the system is capable of surface flipping without adversely impacting electronic device functionality, such as electronic devices comprising arrays of sensors, actuators, or both sensors and actuators.

  6. Appendage mountable electronic devices conformable to surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, John; Ying, Ming; Bonifas, Andrew; Lu, Nanshu

    2017-01-24

    Disclosed are appendage mountable electronic systems and related methods for covering and conforming to an appendage surface. A flexible or stretchable substrate has an inner surface for receiving an appendage, including an appendage having a curved surface, and an opposed outer surface that is accessible to external surfaces. A stretchable or flexible electronic device is supported by the substrate inner and/or outer surface, depending on the application of interest. The electronic device in combination with the substrate provides a net bending stiffness to facilitate conformal contact between the inner surface and a surface of the appendage provided within the enclosure. In an aspect, the system is capable of surface flipping without adversely impacting electronic device functionality, such as electronic devices comprising arrays of sensors, actuators, or both sensors and actuators.

  7. Electron Traps at the Ice Surface

    Science.gov (United States)

    Bockstedte, Michel; Auburger, Philipp; Michl, Anja

    Water, water clusters and ice possess the fascinating ability to solvate electrons. On the surface of water cluster1 and thin crystalline ice structures on a metal substrate2 long-living solvated electron states were observed that evolve from pre-existing surface traps. The identification of such traps provides important insight into the electronic structure of the water or ice surface, and the dissociative interaction of electrons with adsorbates. Models2,3 based on the bilayer terminated Ih-(0001) surface related such traps to orientational defects or vacancies. So far, the understanding of the electronic structure of the ice surface with the electron traps is incomplete. Here we address this issue including also water ad-structures4 within hybrid density functional theory and many-body perturbation theory (G0W0). We identify a hierachy of traps with increasing vertical electron affinity, ranging from hexagon adrows to clusters of orientational defects and vacancies with dangling OH-groups. Siefermann and Abel, Angew. Chem. Int. Ed. 50, 5264 (2011). Bovensiepen et al., J. Chem. Phys. C 113, 979 (2013). Hermann et al., J. Phys.: cond. matter 20, 225003 (2008). Mehlhorn and Morgenstern, Phys. Rev. Lett. 99, 246101 (2007)

  8. Sea Surface Temperature from EUMETSAT Including Sentinel-3 SLSTR

    Science.gov (United States)

    O'Carroll, Anne; Bonekamp, Hans; Montagner, Francois; Santacesaria, Vincenzo; Tomazic, Igor

    2015-12-01

    The paper gives an overview of sea surface temperature (SST) activities at EUMETSAT including information on SST planned from the Sea and Land Surface Temperature Radiometer (SLSTR). Operational oceanography activities within the Marine Applications group at EUMETSAT continue with a focus on SST, sea surface winds, sea-ice products, radiative fluxes, significant wave height and sea surface topography. These are achieved through the mandatory, optional and third-party programmes, and for some products with the EUMETSAT Ocean and Sea-Ice Satellite Application Facility (OSI SAF). Progress towards products from sea-ice surface temperature, ocean colour products, turbidity and aerosol optical depth over water continue. Information on oceanography products from EUMETSAT can be found through the product navigator (http://navigator.eumetsat.int). EUMETSAT have been collaborating with ESA for a number of years on the development of SST for SLSTR.

  9. Molecular Dynamics Simulations of Shocks Including Electronic Heat Conduction and Electron-Phonon Coupling

    Science.gov (United States)

    Ivanov, Dmitriy S.; Zhigilei, Leonid V.; Bringa, Eduardo M.; De Koning, Maurice; Remington, Bruce A.; Caturla, Maria Jose; Pollaine, Stephen M.

    2004-07-01

    Shocks are often simulated using the classical molecular dynamics (MD) method in which the electrons are not included explicitly and the interatomic interaction is described by an effective potential. As a result, the fast electronic heat conduction in metals and the coupling between the lattice vibrations and the electronic degrees of freedom can not be represented. Under conditions of steep temperature gradients that can form near the shock front, however, the electronic heat conduction can play an important part in redistribution of the thermal energy in the shocked target. We present the first atomistic simulation of a shock propagation including the electronic heat conduction and electron-phonon coupling. The computational model is based on the two-temperature model (TTM) that describes the time evolution of the lattice and electron temperatures by two coupled non-linear differential equations. In the combined TTM-MD method, MD substitutes the TTM equation for the lattice temperature. Simulations are performed with both MD and TTM-MD models for an EAM Al target shocked at 300 kbar. The target includes a tilt grain boundary, which provides a region where shock heating is more pronounced and, therefore, the effect of the electronic heat conduction is expected to be more important. We find that the differences between the predictions of the MD and TTM-MD simulations are significantly smaller as compared to the hydrodynamics calculations performed at similar conditions with and without electronic heat conduction.

  10. Ceramic substrate including thin film multilayer surface conductor

    Science.gov (United States)

    Wolf, Joseph Ambrose; Peterson, Kenneth A.

    2017-05-09

    A ceramic substrate comprises a plurality of ceramic sheets, a plurality of inner conductive layers, a plurality of vias, and an upper conductive layer. The ceramic sheets are stacked one on top of another and include a top ceramic sheet. The inner conductive layers include electrically conductive material that forms electrically conductive features on an upper surface of each ceramic sheet excluding the top ceramic sheet. The vias are formed in each of the ceramic sheets with each via being filled with electrically conductive material. The upper conductive layer includes electrically conductive material that forms electrically conductive features on an upper surface of the top ceramic sheet. The upper conductive layer is constructed from a stack of four sublayers. A first sublayer is formed from titanium. A second sublayer is formed from copper. A third sublayer is formed from platinum. A fourth sublayer is formed from gold.

  11. Parabasal theory for plane-symmetric systems including freeform surfaces

    Science.gov (United States)

    Abd El-Maksoud, Rania H.; Hillenbrand, Matthias; Sinzinger, Stefan

    2014-03-01

    An extension of paraxial theory to systems with a single plane of symmetry is provided. This parabasal model is based on the evaluation of a differential region around the reference ray that is defined by the center of the object and the center of the stop. To include freeform surfaces in this model, the local curvatures at the intersection point of the reference ray and the surface are evaluated. As an application, a generalized Scheimpflug principle is presented. The validity of the derived formulas is tested for highly tilted surfaces and is in good agreement with the exact ray tracing results. The analytical expressions are used to provide a first-order layout design of a planar imaging system.

  12. Optical Conductivity of Graphene Sheet Including Electron-Phonon Interaction

    Institute of Scientific and Technical Information of China (English)

    Hamze Mousavi

    2012-01-01

    Using an expression of optical conductivity, based on the linear response theory, the Green's function technique and within the Holstein Hamiltonian model, the effect of electron-phonon interaction on the optical conductivity of graphene plane is studied. It is found that the electron-phonon coupling increases the optical conductivity of graphene sheet in the low frequency region due to decreasing quasiparticle weight of electron excitation while the optical conductivity reduces in the high frequency region. The latter is due to role of electrical field's frequency.

  13. 77 FR 18860 - Certain Consumer Electronics, Including Mobile Phones and Tablets; Notice of Receipt of Complaint...

    Science.gov (United States)

    2012-03-28

    ... COMMISSION Certain Consumer Electronics, Including Mobile Phones and Tablets; Notice of Receipt of Complaint... complaint entitled Certain Consumer Electronics, Including Mobile Phones and Tablets, DN 2885; the... importation of certain consumer electronics, including mobile phones and tablets. The complaint names...

  14. 78 FR 1247 - Certain Electronic Devices, Including Wireless Communication Devices, Tablet Computers, Media...

    Science.gov (United States)

    2013-01-08

    ... COMMISSION Certain Electronic Devices, Including Wireless Communication Devices, Tablet Computers, Media... importation of certain electronic devices, including wireless communication devices, tablet computers, media... United States after importation of certain electronic devices, including wireless communication...

  15. Surfaces and interfaces of electronic materials

    CERN Document Server

    Brillson, Leonard J

    2012-01-01

    An advanced level textbook covering geometric, chemical, and electronic structure of electronic materials, and their applications to devices based on semiconductor surfaces, metal-semiconductor interfaces, and semiconductor heterojunctions. Starting with the fundamentals of electrical measurements on semiconductor interfaces, it then describes the importance of controlling macroscopic electrical properties by atomic-scale techniques. Subsequent chapters present the wide range of surface and interface techniques available to characterize electronic, optical, chemical, and structural propertie

  16. Photoelectron spectroscopy bulk and surface electronic structures

    CERN Document Server

    Suga, Shigemasa

    2014-01-01

    Photoelectron spectroscopy is now becoming more and more required to investigate electronic structures of various solid materials in the bulk, on surfaces as well as at buried interfaces. The energy resolution was much improved in the last decade down to 1 meV in the low photon energy region. Now this technique is available from a few eV up to 10 keV by use of lasers, electron cyclotron resonance lamps in addition to synchrotron radiation and X-ray tubes. High resolution angle resolved photoelectron spectroscopy (ARPES) is now widely applied to band mapping of materials. It attracts a wide attention from both fundamental science and material engineering. Studies of the dynamics of excited states are feasible by time of flight spectroscopy with fully utilizing the pulse structures of synchrotron radiation as well as lasers including the free electron lasers (FEL). Spin resolved studies also made dramatic progress by using higher efficiency spin detectors and two dimensional spin detectors. Polarization depend...

  17. Surface-electronic-state effects in electron emission from the Be(0001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Archubi, C. D. [Instituto de Astronomia y Fisica del Espacio, casilla de correo 67, sucursal 28, C1428EGA, Buenos Aires (Argentina); Gravielle, M. S. [Instituto de Astronomia y Fisica del Espacio, casilla de correo 67, sucursal 28, C1428EGA, Buenos Aires (Argentina); Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Silkin, V. M. [Donostia International Physics Center, E-20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Quimicas, Universidad del Pais Vasco, Apartado 1072, E-20080 San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain)

    2011-07-15

    We study the electron emission produced by swift protons impinging grazingly on a Be(0001) surface. The process is described within a collisional formalism using the band-structure-based (BSB) approximation to represent the electron-surface interaction. The BSB model provides an accurate description of the electronic band structure of the solid and the surface-induced potential. Within this approach we derive both bulk and surface electronic states, with these latter characterized by a strong localization at the crystal surface. We found that such surface electronic states play an important role in double-differential energy- and angle-resolved electron emission probabilities, producing noticeable structures in the electron emission spectra.

  18. Nonlocal bacterial electron transfer to hematite surfaces

    Science.gov (United States)

    Rosso, Kevin M.; Zachara, John M.; Fredrickson, Jim K.; Gorby, Yuri A.; Smith, Steven C.

    2003-03-01

    Mechanisms by which dissimilatory iron-reducing bacteria utilize iron and manganese oxide minerals as terminal electron acceptors for respiration are poorly understood. In the absence of exogenous electron shuttle compounds, extracellular electron transfer is generally thought to occur through the interfacial contact area between mineral surfaces and attached cells. Possible alternative reduction pathways have been proposed based on the discovery of a link between an excreted quinone and dissimilatory reduction. In this study, we utilize a novel experimental approach to demonstrate that Shewanella putrefaciens reduces the surface of crystalline iron oxides at spatial locations that are distinct from points of attachment.

  19. 78 FR 13895 - Certain Consumer Electronics, Including Mobile Phones and Tablets; Commission Determination Not...

    Science.gov (United States)

    2013-03-01

    ... COMMISSION Certain Consumer Electronics, Including Mobile Phones and Tablets; Commission Determination Not To... importation, or sale within the United States after importation of certain consumer electronics, including...''); LG Electronics, Inc. of Seoul, Republic of Korea, LG Electronics U.S.A., Inc. of Englewood...

  20. Elements including metals in the atomizer and aerosol of disposable electronic cigarettes and electronic hookahs.

    Science.gov (United States)

    Williams, Monique; Bozhilov, Krassimir; Ghai, Sanjay; Talbot, Prue

    2017-01-01

    Our purpose was to quantify 36 inorganic chemical elements in aerosols from disposable electronic cigarettes (ECs) and electronic hookahs (EHs), examine the effect of puffing topography on elements in aerosols, and identify the source of the elements. Thirty-six inorganic chemical elements and their concentrations in EC/EH aerosols were determined using inductively coupled plasma optical emission spectroscopy, and their source was identified by analyzing disassembled atomizers using scanning electron microscopy and energy dispersive X-ray spectroscopy. Of 36 elements screened, 35 were detected in EC/EH aerosols, while only 15 were detected in conventional tobacco smoke. Some elements/metals were present in significantly higher concentrations in EC/EH aerosol than in cigarette smoke. Concentrations of particular elements/metals within EC/EH brands were sometimes variable. Aerosols generated at low and high air-flow rates produced the same pattern of elements, although the total element concentration decreased at the higher air flow rate. The relative amount of elements in the first and last 60 puffs was generally different. Silicon was the dominant element in aerosols from all EC/EH brands and in cigarette smoke. The elements appeared to come from the filament (nickel, chromium), thick wire (copper coated with silver), brass clamp (copper, zinc), solder joints (tin, lead), and wick and sheath (silicon, oxygen, calcium, magnesium, aluminum). Lead was identified in the solder and aerosol of two brands of EHs (up to 0.165 μg/10 puffs). These data show that EC/EH aerosols contain a mixture of elements, including heavy metals, with concentrations often significantly higher than in conventional cigarette smoke. While the health effects of inhaling mixtures of heated metals is currently not known, these data will be valuable in future risk assessments involving EC/EH elements/metals.

  1. Development of Surface Acoustic Wave Electronic Nose

    Directory of Open Access Journals (Sweden)

    S.K. Jha

    2010-07-01

    Full Text Available The paper proposes an effective method to design and develop surface acoustic wave (SAW sensor array-based electronic nose systems for specific target applications. The paper suggests that before undertaking full hardware development empirically through hit and trial for sensor selection, it is prudent to develop accurate sensor array simulator for generating synthetic data and optimising sensor array design and pattern recognition system. The latter aspects are most time-consuming and cost-intensive parts in the development of an electronic nose system. This is because most of the electronic sensor platforms, circuit components, and electromechanical parts are available commercially-off-the-shelve (COTS, whereas knowledge about specific polymers and data analysis software are often guarded due to commercial or strategic interests. In this study, an 11-element SAW sensor array is modelled to detect and identify trinitrotoluene (TNT and dinitrotoluene (DNT explosive vapours in the presence of toluene, benzene, di-methyl methyl phosphonate (DMMP and humidity as interferents. Additive noise sources and outliers were included in the model for data generation. The pattern recognition system consists of: (i a preprocessor based on logarithmic data scaling, dimensional autoscaling, and singular value decomposition-based denoising, (ii principal component analysis (PCA-based feature extractor, and (iii an artificial neural network (ANN classifier. The efficacy of this approach is illustrated by presenting detailed PCA analysis and classification results under varied conditions of noise and outlier, and by analysing comparative performance of four classifiers (neural network, k-nearest neighbour, naïve Bayes, and support vector machine.Defence Science Journal, 2010, 60(4, pp.364-376, DOI:http://dx.doi.org/10.14429/dsj.60.493

  2. 78 FR 32689 - Certain Portable Electronic Communications Devices, Including Mobile Phones and Components...

    Science.gov (United States)

    2013-05-31

    ... COMMISSION Certain Portable Electronic Communications Devices, Including Mobile Phones and Components Thereof... communications devices, including mobile phones and components thereof. The complaint names as respondents HTC... Trade Commission has received a complaint entitled Certain Portable Electronic Communications...

  3. 77 FR 60720 - Certain Electronic Devices, Including Wireless Commmunication Devices, Portable Music and Data...

    Science.gov (United States)

    2012-10-04

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION Certain Electronic Devices, Including Wireless Commmunication Devices, Portable Music and Data... infringing electronic devices, including wireless communication devices, portable music and data processing...

  4. 77 FR 27078 - Certain Electronic Devices, Including Mobile Phones and Tablet Computers, and Components Thereof...

    Science.gov (United States)

    2012-05-08

    ... Trade Commission has received a complaint entitled Certain Electronic Devices, Including Mobile Phones... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION Certain Electronic Devices, Including Mobile Phones and Tablet Computers, and Components...

  5. Including Finite Surface Span Effects in Empirical Jet-Surface Interaction Noise Models

    Science.gov (United States)

    Brown, Clifford A.

    2016-01-01

    The effect of finite span on the jet-surface interaction noise source and the jet mixing noise shielding and reflection effects is considered using recently acquired experimental data. First, the experimental setup and resulting data are presented with particular attention to the role of surface span on far-field noise. These effects are then included in existing empirical models that have previously assumed that all surfaces are semi-infinite. This extended abstract briefly describes the experimental setup and data leaving the empirical modeling aspects for the final paper.

  6. Surface acoustic wave devices including Langmuir-Blodgett films (Review)

    Science.gov (United States)

    Plesskii, V. P.

    1991-06-01

    Recent theoretical and experimental research related to the use of Langmuir-Blodgett (LB) films in surface acoustic wave (SAW) devices is reviewed. The sensitivity of the different cuts of quartz and lithium niobate to inertial loading is investigated, and it is shown that some cuts in lithium niobate are twice as sensitive to mass loading than the commonly used YZ-cut. The large variety of organic compounds suitable for the production of LB films makes it possible to create SAW sensors reacting selectively to certain substances. The existing SAW sensors based on LB films are characterized by high sensitivity and fast response.

  7. Hydrodynamics of interaction of particles (including cells) with surfaces

    Science.gov (United States)

    Duszyk, Marek; Doroszewski, Jan

    The study of the phenomena related to the motion of particles flowing in the proximity of the wall is pursued for purely cognitive reason as well as for some important practical purposes in various fields of technology, biology and medicine. When small spherical rigid particles move in the direction parallel to the surface their velocity is smaller than that of the fluid and depends on the ratio of the distance from the wall to the particle radius. The velocity of a particle falling down in a vertical cylinder is maximal in an eccentric position. A sphere in contact with the wall remains stationary. Translational velocity of spherical rigid particles the dimension of which are comparable to that of the tube is only slightly dependent of their lateral position. The differences in the flow parameters of deformable particles in comparison with rigid ones depend on the particle and fluid viscosity coefficient. When the particles move perpendicularly toward the wall, their velocity decreases as the particle approaches the surface. The change of particle velocity is inversely proportional to the gap. There are several theories explaining the influence of the channel diameter on the suspension viscosity (sigma phenomenon); a modern approach is based on the analysis of rheological properties of suspensions. The explanations of the Fahraeus effect (i.e. the fact that the concentration of particles flowing in a tube linking two containers are smaller than that in the containers) are based on non-uniform particle distribution in a transverse cross section and on the differences of velocities of particles and medium. The deviation of the velocity profile of a suspension of rigid particles flowing through a tube from the parabolic shape (blunting) does not depend on the flow velocity; as concerns deformable particles, however, this effect is the smaller the greater is the flow velocity. When the Reynolds number for particles is greater than 10 -3, there appears a component of

  8. Atomic arrangements and electronic properties of semiconductor surfaces and interfaces

    Science.gov (United States)

    Chadi, D. J.; Martin, R. M.

    1982-05-01

    The areas of research during the past 12 months have included: step-formation energies and domain orientation at Si(111) surfaces; the electronic structure of the Al-GaAs(110) surface chemisorption system; density-functional calculations of bulk properties of GaAs and of (100)GaAs-Ge interfaces; demonstration of the importance of correlation effects on the atomic and electronic structure of Si(111) surfaces; and derivation of an exact scaling law for the resistance of a thin wire for the one dimensional Anderson model containing Loth diagonal and off-diagonal disorder.

  9. Surface structure and electronic properties of materials

    Science.gov (United States)

    Siekhaus, W. J.; Somorjai, G. A.

    1975-01-01

    A surface potential model is developed to explain dopant effects on chemical vapor deposition. Auger analysis of the interaction between allotropic forms of carbon and silicon films has shown Si-C formation for all forms by glassy carbon. LEED intensity measurements have been used to determine the mean square displacement of surface atoms of silicon single crystals, and electron loss spectroscopy has shown the effect of structure and impurities on surface states located within the band gap. A thin film of Al has been used to enhance film crystallinity at low temperature.

  10. Electric field distribution of electron emitter surfaces

    Science.gov (United States)

    Tagawa, M.; Takenobu, S.; Ohmae, N.; Umeno, M.

    1987-03-01

    The electric field distribution of a tungsten field emitter surface and a LaB6 thermionic emitter surface has been studied. The computer simulation of electric field distribution on the emitter surface was carried out with a charge simulation method. The electric field distribution of the LaB6 thermionic emitter was experimentally evaluated by the Schottky plot. Two independent equations are necessary for obtaining local electric field and work function; the Fowler-Nordheim equation and the equation of total energy distribution of emitted electron being used to evaluate the electric field distribution of the tungsten field emitter. The experimental results agreed with the computer simulation.

  11. Gutzwiller charge phase diagram of cuprates, including electron-phonon coupling effects

    Science.gov (United States)

    Markiewicz, R. S.; Seibold, G.; Lorenzana, J.; Bansil, A.

    2015-02-01

    Besides significant electronic correlations, high-temperature superconductors also show a strong coupling of electrons to a number of lattice modes. Combined with the experimental detection of electronic inhomogeneities and ordering phenomena in many high-Tc compounds, these features raise the question as to what extent phonons are involved in the associated instabilities. Here we address this problem based on the Hubbard model including a coupling to phonons in order to capture several salient features of the phase diagram of hole-doped cuprates. Charge degrees of freedom, which are suppressed by the large Hubbard U near half-filling, are found to become active at a fairly low doping level. We find that possible charge order is mainly driven by Fermi surface nesting, with competition between a near-(π ,π ) order at low doping and antinodal nesting at higher doping, very similar to the momentum structure of magnetic fluctuations. The resulting nesting vectors are generally consistent with photoemission and tunneling observations, evidence for charge density wave order in YBa2Cu3O7-δ including Kohn anomalies, and suggestions of competition between one- and two-q-vector nesting.

  12. 77 FR 24514 - Certain Consumer Electronics, Including Mobile Phones and Tablets; Institution of Investigation...

    Science.gov (United States)

    2012-04-24

    ... COMMISSION Certain Consumer Electronics, Including Mobile Phones and Tablets; Institution of Investigation... consumer electronics, including mobile phones and tablets, by reason of infringement of certain claims of U... importation, or the sale within the United States after importation of certain consumer electronics,...

  13. 78 FR 48468 - Delphi Corporation, Electronics and Safety Division, Including On-Site Leased Workers From...

    Science.gov (United States)

    2013-08-08

    ... Employment and Training Administration Delphi Corporation, Electronics and Safety Division, Including On-Site... to workers of Delphi Corporation, Electronics and Safety Division, including on-site leased workers... Delphi Corporation, Electronics and Safety Division. The Department has determined that these...

  14. Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

    Directory of Open Access Journals (Sweden)

    Noor A. Nama

    2010-01-01

    Full Text Available Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001-(1×1 surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.

  15. Electron beam induced surface activation of oxide surfaces for nanofabrication

    Energy Technology Data Exchange (ETDEWEB)

    Vollnhals, Florian; Seiler, Steffen; Walz, Marie-Madeleine; Steinrueck, Hans-Peter; Marbach, Hubertus [Lehrstuhl fuer Physikalische Chemie II and Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universitaet Erlangen-Nuernberg, Erlangen (Germany); Woolcot, Tom; Thornton, Geoff [London Centre for Nanotechnology and Department of Chemistry, University College London (United Kingdom)

    2012-07-01

    The controlled fabrication of structures on the nanoscale is a major challenge in science and engineering. Direct-write techniques like Electron Beam Induced Deposition (EBID) were shown to be suitable tools in this context. Recently, Electron Beam Induced Surface Activation (EBISA) has been introduced as a new focused electron beam technique. In EBISA, a surface, e.g. SiO{sub 2}, is irradiated by a focused electron beam, resulting in an activation of the exposed area. The activated area can then react and decompose precursor gases like iron pentacarbonyl, Fe(CO){sub 5}. This leads to a primary deposit, which continues to grow autocatalytically as long as Fe(CO){sub 5} is supplied, resulting in pure (> 90 % at.), crystalline iron nanostructures. We expand the use of this concept by exploring EBISA to produce metallic nanostructures on TiO{sub 2}(110) in UHV; atomistic insight into the process is obtained via Scanning Tunneling Microscopy (STM) and chemical insight via Auger Electron Spectroscopy (AES).

  16. A surface-electrode quadrupole guide for electrons

    Energy Technology Data Exchange (ETDEWEB)

    Hoffrogge, Johannes Philipp

    2012-12-19

    This thesis reports on the design and first experimental realization of a surface-electrode quadrupole guide for free electrons. The guide is based on a miniaturized, planar electrode layout and is driven at microwave frequencies. It confines electrons in the near-field of the microwave excitation, where strong electric field gradients can be generated without resorting to resonating structures or exceptionally high drive powers. The use of chip-based electrode geometries allows the realization of versatile, microstructured potentials with the perspective of novel quantum experiments with guided electrons. I present the design, construction and operation of an experiment that demonstrates electron confinement in a planar quadrupole guide for the first time. To this end, electrons with kinetic energies from one to ten electron-volts are guided along a curved electrode geometry. The stability of electron guiding as a function of drive parameters and electron energy has been studied. A comparison with numerical particle tracking simulations yields good qualitative agreement and provides a deeper understanding of the electron dynamics in the guiding potential. Furthermore, this thesis gives a detailed description of the design of the surface-electrode layout. This includes the development of an optimized coupling structure to inject electrons into the guide with minimum transverse excitation. I also discuss the extension of the current setup to longitudinal guide dimensions that are comparable to or larger than the wavelength of the drive signal. This is possible with a modified electrode layout featuring elevated signal conductors. Electron guiding in the field of a planar, microfabricated electrode layout allows the generation of versatile and finely structured guiding potentials. One example would be the realization of junctions that split and recombine a guided electron beam. Furthermore, it should be possible to prepare electrons in low-lying quantum mechanical

  17. Observation of Hot Electrons in Surface-Wave Plasmas Excited by Surface Plasmon Polaritons

    Institute of Scientific and Technical Information of China (English)

    HU Ye-Lin; CHEN Zhao-Quan; LIU Ming-Hai; HONG Ling-Li; LI Ping; ZHENG Xiao-Liang; XIA Guang-Qing; HU Xi-Wei

    2011-01-01

    The electron energy distribution functions (EEDFs) are studied in the planar-type surface-wave plasma (SWP)caused by resonant excitation of surface plasmon polaritons (SPPs) using a single cylindrical probe.Sustained plasma characteristics can be considered as a bi-Maxwellian EEDF,which correspond to a superposition of the bulk low-temperature electron and the high-energy electron beam-like part.The beam component energy is pronounced at about 10eV but the bulk part is lower than 3.5eV.The hot electrons included in the proposed plasmas play a significant role in plasma heating and further affect the discharge chemistry.During the past several years,in the fabrication ofamorphous or crystalline silicon films,diamond film synthesis and carbon nanotube growth,the large-area overdense plasma source has been useful.In electronic device fabrication techniques such as etching,ashing or plasma chemical vapor deposition,overdense electrons and radicals are required,especially hot electrons.Among the various plasma devices,the planar-type surface-wave plasma (SWP) source is an advanced plasma source,which is a type of promising plasma source satisfying the above rigorous requirements for large-area plasma processing.%The electron energy distribution functions (EEDFs) are studied in the planar-type surface-wave plasma (SWP) caused by resonant excitation of surface plasmon polaritons (SPPs) using a single cylindrical probe. Sustained plasma characteristics can be considered as a bi-Maxwellian EEDF, which correspond to a superposition of the bulk low-temperature electron and the high-energy electron beam-like part. The beam component energy is pronounced at about 10 eV but the bulk part is lower than 3.5 eV. The hot electrons included in the proposed plasmas play a significant role in plasma heating and further affect the discharge chemistry.

  18. Treatment of surfaces with low-energy electrons

    Science.gov (United States)

    Frank, L.; Mikmeková, E.; Lejeune, M.

    2017-06-01

    Electron-beam-induced deposition of various materials from suitable precursors has represented an established branch of nanotechnology for more than a decade. A specific alternative is carbon deposition on the basis of hydrocarbons as precursors that has been applied to grow various nanostructures including masks for subsequent technological steps. Our area of study was unintentional electron-beam-induced carbon deposition from spontaneously adsorbed hydrocarbon molecules. This process traditionally constitutes a challenge for scanning electron microscopy practice preventing one from performing any true surface studies outside an ultrahigh vacuum and without in-situ cleaning of samples, and also jeopardising other electron-optical devices such as electron beam lithographs. Here we show that when reducing the energy of irradiating electrons sufficiently, the e-beam-induced deposition can be converted to e-beam-induced release causing desorption of hydrocarbons and ultimate cleaning of surfaces in both an ultrahigh and a standard high vacuum. Using series of experiments with graphene samples, we demonstrate fundamental features of e-beam-induced desorption and present results of checks for possible radiation damage using Raman spectroscopy that led to optimisation of the electron energy for damage-free cleaning. The method of preventing carbon contamination described here paves the way for greatly enhanced surface sensitivity of imaging and substantially reduced demands on vacuum systems for nanotechnological applications.

  19. Surface and grain boundary scattering in nanometric Cu thin films: A quantitative analysis including twin boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Barmak, Katayun [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 and Department of Materials Science and Engineering and Materials Research Science and Engineering Center, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Darbal, Amith [Department of Materials Science and Engineering and Materials Research Science and Engineering Center, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Ganesh, Kameswaran J.; Ferreira, Paulo J. [Materials Science and Engineering, The University of Texas at Austin, 1 University Station, Austin, Texas 78712 (United States); Rickman, Jeffrey M. [Department of Materials Science and Engineering and Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015 (United States); Sun, Tik; Yao, Bo; Warren, Andrew P.; Coffey, Kevin R., E-mail: kb2612@columbia.edu [Department of Materials Science and Engineering, University of Central Florida, 4000 Central Florida Boulevard, Orlando, Florida 32816 (United States)

    2014-11-01

    The relative contributions of various defects to the measured resistivity in nanocrystalline Cu were investigated, including a quantitative account of twin-boundary scattering. It has been difficult to quantitatively assess the impact twin boundary scattering has on the classical size effect of electrical resistivity, due to limitations in characterizing twin boundaries in nanocrystalline Cu. In this study, crystal orientation maps of nanocrystalline Cu films were obtained via precession-assisted electron diffraction in the transmission electron microscope. These orientation images were used to characterize grain boundaries and to measure the average grain size of a microstructure, with and without considering twin boundaries. The results of these studies indicate that the contribution from grain-boundary scattering is the dominant factor (as compared to surface scattering) leading to enhanced resistivity. The resistivity data can be well-described by the combined Fuchs–Sondheimer surface scattering model and Mayadas–Shatzkes grain-boundary scattering model using Matthiessen's rule with a surface specularity coefficient of p = 0.48 and a grain-boundary reflection coefficient of R = 0.26.

  20. 78 FR 34132 - Certain Portable Electronic Communications Devices, Including Mobile Phones and Components...

    Science.gov (United States)

    2013-06-06

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION Certain Portable Electronic Communications Devices, Including Mobile Phones and Components Thereof... Communications Devices, Including Mobile Phones and Components Thereof, DN 2958; the Commission...

  1. 78 FR 16865 - Certain Electronic Devices, Including Wireless Communication Devices, Portable Music and Data...

    Science.gov (United States)

    2013-03-19

    ... COMMISSION Certain Electronic Devices, Including Wireless Communication Devices, Portable Music and Data... importation of certain electronic devices, including wireless communication devices, portable music and data... infringe the asserted claims of the '348 patent affect the public interest, as identified in 19 U.S.C....

  2. 77 FR 70464 - Certain Electronic Devices, Including Wireless Communication Devices, Portable Music and Data...

    Science.gov (United States)

    2012-11-26

    ... COMMISSION Certain Electronic Devices, Including Wireless Communication Devices, Portable Music and Data... importation of certain electronic devices, including wireless communication devices, portable music and data... either are adversely affecting it or likely to do so. For background, see Certain Devices for...

  3. Electronic Structure and Catalysis on Metal Surfaces

    Science.gov (United States)

    Greeley, Jeff; Norskov, Jens K.; Mavrikakis, Manos

    2002-10-01

    The powerful computational resources available to scientists today, together with recent improvements in electronic structure calculation algorithms, are providing important new tools for researchers in the fields of surface science and catalysis. In this review, we discuss first principles calculations that are now capable of providing qualitative and, in many cases, quantitative insights into surface chemistry. The calculations can aid in the establishment of chemisorption trends across the transition metals, in the characterization of reaction pathways on individual metals, and in the design of novel catalysts. First principles studies provide an excellent fundamental complement to experimental investigations of the above phenomena and can often allow the elucidation of important mechanistic details that would be difficult, if not impossible, to determine from experiments alone.

  4. 75 FR 448 - In the Matter of: Certain Authentication Systems, Including Software and Handheld Electronic...

    Science.gov (United States)

    2010-01-05

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION In the Matter of: Certain Authentication Systems, Including Software and Handheld Electronic Devices; Notice of Investigation AGENCY: U.S. International Trade Commission. ACTION: Institution...

  5. Some unusual electronic patterns on graphite surface

    Indian Academy of Sciences (India)

    Shyam K Choudhury; Anjan K Gupta

    2008-02-01

    We report on the observation of some unusual electronic patterns on a graphite surface using scanning tunneling spectroscopy (STM). We attribute these patterns to different types of strain near the surface. One such pattern seen on a particular layer comprises of two-dimensional spatially varying super-lattice and one-dimensional fringes. This pattern is present in a finite region of a layer on the surface confined between two carbon fibers. We attribute this spatially varying super-lattice structure to the shear strain generated in the top layer due to the restraining fibers. We have also developed a model with the Moirµe rotation hypothesis that gives us a better insight into such large-scale spatially varying patterns. We have been able to model the above-observed pattern. We also report another pattern near a defect, which we attribute to the change in density of states due to the physical buckling of the top graphite layer. Part of this buckled layer is found to be buried under another layer and this region shows a reversed contrast and thus supporting our idea of buckling. We also performed tunneling spectroscopy measurements on various regions of these patterns which show significant variations in the density of states.

  6. 17 CFR 232.104 - Unofficial PDF copies included in an electronic submission.

    Science.gov (United States)

    2010-04-01

    ... 17 Commodity and Securities Exchanges 2 2010-04-01 2010-04-01 false Unofficial PDF copies included... Filing Requirements § 232.104 Unofficial PDF copies included in an electronic submission. (a) An... (§ 249.101 of this chapter) or a Form D (§ 239.500 of this chapter), may include one unofficial PDF copy...

  7. Self-consistent many-electron theory of electron work functions and surface potential characteristics for selected metals

    Science.gov (United States)

    Smith, J. R.

    1969-01-01

    Electron work functions, surface potentials, and electron number density distributions and electric fields in the surface region of 26 metals were calculated from first principles within the free electron model. Calculation proceeded from an expression of the total energy as a functional of the electron number density, including exchange and correlation energies, as well as a first inhomogeneity term. The self-consistent solution was obtained via a variational procedure. Surface barriers were due principally to many-body effects; dipole barriers were small only for some alkali metals, becoming quite large for the transition metals. Surface energies were inadequately described by this model, which neglects atomistic effects. Reasonable results were obtained for electron work functions and surface potential characteristics, maximum electron densities varying by a factor of over 60.

  8. Generation of surface electrons in femtosecond laser-solid interactions

    Institute of Scientific and Technical Information of China (English)

    XU; Miaohua; LI; Yutong; YUAN; Xiaohui; ZHENG; Zhiyuan; LIANG; Wenxi; YU; Quanzhi; ZHANG; Yi; WANG; Zhaohua; WEI; Zhiyi; ZHANG; Jie

    2006-01-01

    The characteristics of hot electrons produced by p-polarized femtosecond laser-solid interactions are studied. The experimental results show that the outgoing electrons are mainly emitted in three directions: along the target surface, the normal direction and the laser backward direction. The electrons flowing along the target surface are due to the confinement of the electrostatic field and the surface magnetic field, while the electrons in the normal direction due to the resonant absorption.

  9. Electron beam induced oxidation of Al–Mg alloy surfaces

    NARCIS (Netherlands)

    Palasantzas, G.; Agterveld, D.T.L. van; Hosson, J.Th.M. De

    2002-01-01

    Electron beam currents of a few nanoamperes, currently used in nanometer scale scanning Auger/electron microscopy, induces severe oxidation of Al–Mg alloy surfaces at room temperature. Auger peak-to-peak oxygen curves for Al–Mg surfaces support the hypothesis that the electron beam creates

  10. Electron beam induced oxidation of Al–Mg alloy surfaces

    NARCIS (Netherlands)

    Palasantzas, G.; Agterveld, D.T.L. van; Hosson, J.Th.M. De

    2002-01-01

    Electron beam currents of a few nanoamperes, currently used in nanometer scale scanning Auger/electron microscopy, induces severe oxidation of Al–Mg alloy surfaces at room temperature. Auger peak-to-peak oxygen curves for Al–Mg surfaces support the hypothesis that the electron beam creates additiona

  11. An AES Study of the Room Temperature Surface Conditioning of Technological Metal Surfaces by Electron Irradiation

    CERN Document Server

    Scheuerlein, C; Taborelli, M; Brown, A; Baker, M A

    2002-01-01

    The modifications to technological copper and niobium surfaces induced by 2.5 keV electron irradiation have been investigated in the context of the conditioning process occurring in particle accelerator ultra high vacuum systems. Changes in the elemental surface composition have been found using Scanning Auger Microscopy (SAM) by monitoring the carbon, oxygen and metal Auger peak intensities as a function of electron irradiation in the dose range 10-6 to 10-2 C mm-2. The surface analysis results are compared with electron dose dependent secondary electron and electron stimulated desorption yield measurements. Initially the electron irradiation causes a surface cleaning through electron stimulated desorption, in particular of hydrogen. During this period both the electron stimulated desorption and secondary electron yield decrease as a function of electron dose. When the electron dose exceeds 10-4 C mm-2 electron stimulated desorption yields are reduced by several orders of magnitude and the electron beam indu...

  12. On the Convergence of the Electronic Structure Properties of the FCC Americium (001) Surface

    OpenAIRE

    Gao, Da; Ray, Asok K.

    2006-01-01

    Electronic and magnetic properties of the fcc Americium (001) surface have been investigated via full-potential all-electron density-functional electronic structure calculations at both scalar and fully relativistic levels. Effects of various theoretical approximations on the fcc Am (001) surface properties have been thoroughly examined. The ground state of fcc Am (001) surface is found to be anti-ferromagnetic with spin-orbit coupling included (AFM-SO). At the ground state, the magnetic mome...

  13. Electron-beam dynamics in a strong laser field including quantum radiation reaction

    CERN Document Server

    Neitz, Norman

    2014-01-01

    The evolution of an electron beam colliding head-on with a strong plane-wave field is investigated in the framework of strong-field QED including radiation-reaction effects due to photon emission. Employing a kinetic approach to describe the electron and the photon distribution it is shown that at a given total laser fluence the final electron distribution depends on the shape of the laser envelope and on the pulse duration, in contrast to the classical predictions of radiation reaction based on the Landau-Lifshitz equation. Finally, it is investigated how the pair-creation process leads to a nonlinear coupled evolution of the electrons in the beam, of the produced charged particles, and of the emitted photons.

  14. Electron-beam dynamics in a strong laser field including quantum radiation reaction

    Science.gov (United States)

    Neitz, N.; Di Piazza, A.

    2014-08-01

    The evolution of an electron beam colliding head on with a strong plane-wave field is investigated in the framework of strong-field QED including radiation-reaction effects due to photon emission. Employing a kinetic approach to describe the electron and the photon distribution it is shown that at a given total laser fluence the final electron distribution depends on the shape of the laser envelope and on the pulse duration, in contrast to the classical predictions of radiation reaction based on the Landau-Lifshitz equation. Finally, it is investigated how the pair-creation process leads to a nonlinear coupled evolution of the electrons in the beam, of the produced charged particles, and of the emitted photons.

  15. Evaporation of hydrocarbon compounds, including gasoline and diesel fuel, on heated metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Fardad, D.; Ladommatos, N. [Brunel Univ., Dept. of Mechanical Engineering, Uxbridge (United Kingdom)

    1999-11-01

    An investigation was carried out on the evaporation of various hydrocarbon liquids on heated surfaces. Single and multicomponent hydrocarbon compounds were used, including hexane, heptane, octane, a hexane-octane mixture, gasoline and diesel fuel. The heated surface included aluminium, mild steel, cast iron and copper. Tests were also carried out with different surface textures and surface coatings. The motivation for this work was a desire to improve understanding of the evaporation processes taking place in the inlet port and, to a lesser extent, within the combustion chamber of internal combustion engines. The hydrocarbon compounds were released on the heated surfaces as individual small droplets, and the subsequent evaporation was recorded using a CCD (charge coupled device) camera. These observations were then used to ascertain the effects of material, surface temperature, surface textures, surface coating and liquid composition on the heat flux and other aspects of droplet behaviour. (Author)

  16. Electron Conditioning of Technical Aluminium Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Le Pimpec, F

    2004-09-02

    The effect of electron conditioning on commercially aluminium alloys 1100 and 6063 were investigated. Contrary to the assumption that electron conditioning, if performed long enough, can reduce and stabilize the SEY to low values (= 1.3, value of many pure elements [1]), the SEY of aluminium did not go lower than 1.8. In fact, it reincreases with continued electron exposure dose.

  17. Integrated optoelectronic probe including a vertical cavity surface emitting laser for laser Doppler perfusion monitoring

    NARCIS (Netherlands)

    Serov, Alexander N.; Nieland, Janharm; Oosterbaan, Sjoerd; Mul, de Frits F.M.; Kranenburg, van Herma; Bekman, Herman H.P.Th.; Steenbergen, Wiendelt

    2006-01-01

    An integrated optoelectronic probe with small dimensions, for direct-contact laser Doppler blood flow monitoring has been realized. A vertical cavity surface emitting laser (VCSEL), and a chip with photodetectors and all necessary electronics are integrated in a miniature probe head connected to a l

  18. Integrated Optoelectronic Probe Including a Vertical Cavity Surface Emitting Laser for Laser Doppler Perfusion Monitoring

    NARCIS (Netherlands)

    Serov, A.N.; Nieland, J.; Oosterbaan, S.; Steenbergen, W.; Bekman, H.H.P.T.; Mul, F.F.M. de; Kranenburg, H. van

    2006-01-01

    An integrated optoelectronic probe with small dimensions, for direct-contact laser Doppler blood flow monitoring has been realized. A vertical cavity surface emitting laser (VCSEL), and a chip with photodetectors and all necessary electronics are integrated in a miniature probe head connected to a l

  19. Atomic and electronic structure of surfaces theoretical foundations

    CERN Document Server

    Lannoo, Michel

    1991-01-01

    Surfaces and interfaces play an increasingly important role in today's solid state devices. In this book the reader is introduced, in a didactic manner, to the essential theoretical aspects of the atomic and electronic structure of surfaces and interfaces. The book does not pretend to give a complete overview of contemporary problems and methods. Instead, the authors strive to provide simple but qualitatively useful arguments that apply to a wide variety of cases. The emphasis of the book is on semiconductor surfaces and interfaces but it also includes a thorough treatment of transition metals, a general discussion of phonon dispersion curves, and examples of large computational calculations. The exercises accompanying every chapter will be of great benefit to the student.

  20. Surface and volume photoemission of hot electrons from plasmonic nanoantennas

    DEFF Research Database (Denmark)

    Uskov, Alexander V.; Protsenko, Igor E.; Ikhsanov, Renat S.;

    2014-01-01

    We theoretically compare surface- and volume-based photoelectron emission from spherical nanoparticles, obtaining analytical expressions for the emission rate in both mechanisms. We show that the surface mechanism prevails, being unaffected by detrimental hot electron collisions....

  1. Surface and volume photoemission of hot electrons from plasmonic nanoantennas

    DEFF Research Database (Denmark)

    Uskov, Alexander V.; Protsenko, Igor E.; Ikhsanov, Renat S.

    2014-01-01

    We theoretically compare surface- and volume-based photoelectron emission from spherical nanoparticles, obtaining analytical expressions for the emission rate in both mechanisms. We show that the surface mechanism prevails, being unaffected by detrimental hot electron collisions.......We theoretically compare surface- and volume-based photoelectron emission from spherical nanoparticles, obtaining analytical expressions for the emission rate in both mechanisms. We show that the surface mechanism prevails, being unaffected by detrimental hot electron collisions....

  2. Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces

    CERN Document Server

    Bullock, E T

    2000-01-01

    Insulating materials are widely used in electronic devices. Bulk insulators and insulating films pose unique challenges for high resolution study since most commonly used charged particle surface analysis techniques are incompatible with insulating surfaces and materials. A, method of performing scanning tunneling microscopy (STM) on insulating surfaces has been investigated. The method is referred to as electron-beam assisted scanning tunneling microscopy (e-BASTM). It is proposed that by coupling the STM and the scanning electron microscopy (SEM) as one integrated device, that insulating materials may be studied, obtaining both high spatial resolution, and topographic and electronic resolution. The premise of the technique is based on two physical consequences of the interaction of an energetic electron beam (PE) with a material. First, when an electron beam is incident upon a material, low level material electrons are excited into conduction band states. For insulators, with very high secondary electron yi...

  3. Electron diffraction study of {alpha}-AlMnSi crystals including non-crystallographic axes

    Energy Technology Data Exchange (ETDEWEB)

    Song, G.L.; Bursill, L.A.

    1997-06-01

    The structure of crystalline {alpha}-AlMnSi is examined by electron diffraction. Six distinct zone axes are examined, including both normal crystallographic and non-crystallographic zones axes, allowing the space group symmetry to be studied. Electron diffraction patterns characteristic of Pm3-bar were obtained for thicker specimens. However, for very thin specimens, as used for HRTEM imaging, the electron diffraction patterns were characteristic of Im3-bar space group symmetry. The structural basis of the Pm3-bar to Im3-bar transformation may be understood in terms of an analysis of the icosahedral structural elements located at the corners and body-centers of the cubic unit cell. A method for indexing the non-crystallographic zone axis diffraction patterns is described. An electron diffraction pattern of the 5-fold axis of the quasicrystalline phase i-AlMnSi is also included; this is compared with the experimental results and calculations for the [0{tau}1] axis of Pm3-bar and Im3-bar crystalline phases. 26 refs., 4 tabs., 7 figs.

  4. Electronic interconnects and devices with topological surface states and methods for fabricating same

    Energy Technology Data Exchange (ETDEWEB)

    Yazdani, Ali; Ong, N. Phuan; Cava, Robert J.

    2017-04-04

    An interconnect is disclosed with enhanced immunity of electrical conductivity to defects. The interconnect includes a material with charge carriers having topological surface states. Also disclosed is a method for fabricating such interconnects. Also disclosed is an integrated circuit including such interconnects. Also disclosed is a gated electronic device including a material with charge carriers having topological surface states.

  5. Electronic interconnects and devices with topological surface states and methods for fabricating same

    Energy Technology Data Exchange (ETDEWEB)

    Yazdani, Ali; Ong, N. Phuan; Cava, Robert J.

    2016-05-03

    An interconnect is disclosed with enhanced immunity of electrical conductivity to defects. The interconnect includes a material with charge carriers having topological surface states. Also disclosed is a method for fabricating such interconnects. Also disclosed is an integrated circuit including such interconnects. Also disclosed is a gated electronic device including a material with charge carriers having topological surface states.

  6. 77 FR 3499 - Sony Electronics, Inc., Including On-Site Leased Workers From Selectremedy Park Ridge, NJ...

    Science.gov (United States)

    2012-01-24

    ...] Sony Electronics, Inc., Including On-Site Leased Workers From Selectremedy Park Ridge, NJ; Amended... of Sony Electronics, Inc., SEL Headquarters, including on-site leased workers of SelectRemedy, StaffMark, and Payrolling.com , San Diego, California (TA-W-71,501); Sony Electronics, Inc., including...

  7. Electron-Hole Counting Approach to Surface Atomic Structure

    Science.gov (United States)

    Chadi, D. J.

    The observed reconstructions of III-V semiconductor surfaces are shown to be consistent with constraints imposed by a simple "electron-hole" counting rule proposed by Pashley. The rule ensures that the predicted surfaces are nonmetallic, nonpolar, and at least, metastable since the compensation of the "donor" electrons leaves no occupied states in the upper part of the band gap which can easily induce other reconstructions. Applications of the method to the problem of surface structure and passivation are examined.

  8. Nanocoating of titanium implant surfaces with organic molecules. Polysaccharides including glycosaminoglycans

    DEFF Research Database (Denmark)

    Gurzawska, Katarzyna Aleksandra; Svava, Rikke; Jørgensen, Niklas Rye;

    2012-01-01

    Long-term stability of titanium implants are dependent on a variety of factors. Nanocoating with organic molecules is one of the method used to improve osseointegration. Nanoscale modification of titanium implants affects surface properties, such as hydrophilicity, biochemical bonding capacity...... and roughness. This influences cell behaviour on the surface such as adhesion, proliferation and differentiation of cells as well as the mineralization of the extracellular matrix at the implant surfaces. The aim of the present systematic review was to describe organic molecules used for surface nanocoating...... nanocoatings. The included in vivo studies, showed improvement of bone interface reactions measured as increased Bone-to-Implant Contact length and Bone Mineral Density adjacent to the polysaccharide coated surfaces. Based on existing literature, surface modification with polysaccharide and glycosaminoglycans...

  9. Hydrophobicity of electron beam modified surface of hydroxyapatite films

    Energy Technology Data Exchange (ETDEWEB)

    Gregor, M., E-mail: gregor@fmph.uniba.sk [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia); Plecenik, T. [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia); Tofail, S.A.M. [Materials & Surface Science Institute, University of Limerick, Limerick (Ireland); Zahoran, M.; Truchly, M. [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia); Vargova, M. [Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University, 84215 Bratislava (Slovakia); Laffir, F. [Materials & Surface Science Institute, University of Limerick, Limerick (Ireland); Plesch, G. [Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University, 84215 Bratislava (Slovakia); Kus, P.; Plecenik, A. [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia)

    2015-05-15

    Highlights: • Surface potential of hydroxyapatite films were modified by focused electron beam. • Micron-sized domains of modified surface potential were created. • Wettability and surface free energy of the irradiated areas was studied. • Possible mechanisms of increased surface hydrophobicity are discussed. - Abstract: Arrays of micron-sized domains of modified surface potential were created on hydroxyapatite films by mid-energy (20 keV) electron beam irradiation available in a laboratory scanning electron microscope. The dosage of electron beam was varied between 10{sup −3} and 10{sup 3} μC/cm{sup 2} to inject charge into the film surface. Contrary to the conventional electrowetting theory, the dosage of injected charge used in creating such microdomains caused a gradual increase of the water contact angle from 57° to 93° due to the elimination of the polar component of the surface free energy. Surface contamination by carbonaceous species can be held only partially responsible for such behavior at lower dosage of electron beam. A transfer of free surface charge to water and an electron beam induced disruption of polar orientation of OH ions have been attributed to be influencial factors in the overall dewetting behavior.

  10. Electron dynamics at surfaces induced by highly charged ions

    NARCIS (Netherlands)

    Morgenstern, R

    1998-01-01

    Energy spectra of electrons resulting from hydrogen-like multiply charged N6+ and Q(7+) ions on various surfaces are presented and discussed. Por metal target surfaces thr formation and decay of hollow atoms during the approach towards the surface is rather well understood in terms of the classical

  11. Electron dynamics at surfaces induced by highly charged ions

    NARCIS (Netherlands)

    Morgenstern, R

    Energy spectra of electrons resulting from hydrogen-like multiply charged N6+ and Q(7+) ions on various surfaces are presented and discussed. Por metal target surfaces thr formation and decay of hollow atoms during the approach towards the surface is rather well understood in terms of the classical

  12. Phosphogypsum surface characterisation using scanning electron microscopy

    Directory of Open Access Journals (Sweden)

    Rajković Miloš B.

    2003-01-01

    Full Text Available This paper presents the results of application of Scanning Electron Microscopy (SEM to examinations of the samples of natural gypsum and phosphogypsum. Phosphogypsum has a well developed crystalline structure, and appear in two polymorphous forms, of rombic and hexagonal shape crystals. Natural gypsum has a poorly crystalline structure. The differences in crystalline structure influence the chemical behavior of these row materials.

  13. A scanning Auger electron spectrometer for internal surface analysis of Large Electron Positron 2 superconducting radio-frequency cavities

    Energy Technology Data Exchange (ETDEWEB)

    Benvenuti, C.; Cosso, R.; Genest, J.; Hauer, M.; Lacarrere, D.; Rijllart, A.; Saban, R. [CERN, 1211 Geneva 23 (Switzerland)

    1996-08-01

    A computer-controlled surface analysis instrument, incorporating static Auger electron spectroscopy, scanning Auger mapping, and secondary electron imaging, has been designed and built at CERN to study and characterize the inner surface of superconducting radio-frequency cavities to be installed in the Large Electron Positron collider. A detailed description of the instrument, including the analytical head, the control system, and the vacuum system is presented. Some recent results obtained from the cavities provide examples of the instrument{close_quote}s capabilities. {copyright} {ital 1996 American Institute of Physics.}

  14. Electron bombardment of water adsorbed on Zr(0001) surfaces

    CERN Document Server

    Ankrah, S; Ramsier, R D

    2003-01-01

    A study of the effects of electron bombardment on water adsorbed on Zr(0001) is reported. Zirconium surfaces are dosed with isotopic water mixtures at 160 K followed by electron bombardment (485 eV). The system is then probed by low energy electron diffraction, temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). No evidence is found that would indicate preferential mixing of hydrogen from the bulk with isotopic water dissociation products during TPD. However, electron bombardment results in the sharpening of a hydrogen/deuterium desorption peak near 320 K and the production of water near 730 K at low water exposures. In addition, although water does not oxidize Zr(0001) thermally, electron bombardment of adsorbed water induces a shift of about 2 eV in the Zr AES features indicating that the surface is partially oxidized by electron bombardment.

  15. Surface dose with grids in electron beam radiation therapy

    Energy Technology Data Exchange (ETDEWEB)

    Lin, K.-H.; Huang, C.-Y.; Lin, J.-P.; Chu, T.-C. E-mail: tcchu@mx.nthu.edu.tw

    2002-03-01

    This investigation attempts to solve the problem of the lack of skin-sparing effect in electron radiation therapy and to increase the tolerance of skin to radiation using the grid technique. Electron grid therapy involves the mounting of a Cerrobend grid in the electron cone. Film dosimetry was employed to measure the relative surface dose and the percentage depth dose profile of electron grid portals. Various grid hole diameters (d=0.45, 1.0, 1.5 cm) and grid hole spacings (s=0.4, 0.2 cm) were considered for electron beams from 6 to 14 MeV. Experimental results indicate that the electron grid technique can reduce the relative surface dose in electron radiation therapy. Degradations of the relative surface dose depend on the percentage of open area in the grid portal. A proper grid design allows the surface dose to be reduced and the range of nonhomogeneous doses to be limited to a depth at which the target volume can receive a homogeneous dose. The grid technique can lower the surface dose in electron radiation therapy.

  16. Evolution of electron Fermi surface with doping in cobaltates.

    Science.gov (United States)

    Ma, Xixiao; Lan, Yu; Qin, Ling; Kuang, Lülin; Feng, Shiping

    2016-08-24

    The notion of the electron Fermi surface is one of the characteristic concepts in the field of condensed matter physics, and it plays a crucial role in the understanding of the physical properties of doped Mott insulators. Based on the t-J model, we study the nature of the electron Fermi surface in the cobaltates, and qualitatively reproduce the essential feature of the evolution of the electron Fermi surface with doping. It is shown that the underlying hexagonal electron Fermi surface obeys Luttinger's theorem. The theory also predicts a Fermi-arc phenomenon at the low-doped regime, where the region of the hexagonal electron Fermi surface along the [Formula: see text]-K direction is suppressed by the electron self-energy, and then six disconnected Fermi arcs located at the region of the hexagonal electron Fermi surface along the [Formula: see text]-M direction emerge. However, this Fermi-arc phenomenon at the low-doped regime weakens with the increase of doping.

  17. Structural and electronic properties of hydrosilylated silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Baumer, A.

    2005-11-15

    The structural and electronic properties of alkyl-terminated Si surfaces prepared by thermallyinduced hydrosilylation have been studied in detail in the preceding chapters. Various surfaces have been used for the functionalization ranging from crystalline Si over amorphous hydrogenated Si to nanoscaled materials such as Si nanowires and nanoparticles. In each case, the alkyl-terminated surfaces have been compared to the native oxidized and H-terminated surfaces. (orig.)

  18. Hot-electron nanoscopy using adiabatic compression of surface plasmons

    KAUST Repository

    Giugni, Andrea

    2013-10-20

    Surface plasmon polaritons are a central concept in nanoplasmonics and have been exploited to develop ultrasensitive chemical detection platforms, as well as imaging and spectroscopic techniques at the nanoscale. Surface plasmons can decay to form highly energetic (or hot) electrons in a process that is usually thought to be parasitic for applications, because it limits the lifetime and propagation length of surface plasmons and therefore has an adverse influence on the functionality of nanoplasmonic devices. Recently, however, it has been shown that hot electrons produced by surface plasmon decay can be harnessed to produce useful work in photodetection, catalysis and solar energy conversion. Nevertheless, the surface-plasmon-to-hot-electron conversion efficiency has been below 1% in all cases. Here we show that adiabatic focusing of surface plasmons on a Schottky diode-terminated tapered tip of nanoscale dimensions allows for a plasmon-to-hot-electron conversion efficiency of ∼30%. We further demonstrate that, with such high efficiency, hot electrons can be used for a new nanoscopy technique based on an atomic force microscopy set-up. We show that this hot-electron nanoscopy preserves the chemical sensitivity of the scanned surface and has a spatial resolution below 50 nm, with margins for improvement.

  19. Extensive ab initio study of the electronic states of BSe radical including spin-orbit coupling

    Science.gov (United States)

    Liu, Siyuan; Zhai, Hongsheng; Liu, Yufang

    2016-06-01

    The internally contracted multi-reference configuration interaction method (MRCI) with Davidson modification and the Douglas-Kroll scalar relativistic correction has been used to calculate the BSe molecule at the level of aug-cc-pV5Z basis set. The calculated electronic states, including 9 doublet and 6 quartet Λ-S states, are correlated to the dissociation limit of B(2Pu) + Se(3Pg) and B(2Pu) + Se(1Dg). The Spin-orbit coupling (SOC) interaction is taken into account via the state interaction approach with the full Breit-Pauli Hamiltonian operator, which causes the entire 15 Λ-S states to split into 32 Ω states. This is the first time that the spin-orbit coupling calculation has been carried out on BSe. The potential energy curves of the Λ-S and Ω electronic states are depicted with the aid of the avoided crossing rule between electronic states of the same symmetry. The spectroscopic constants of the bound Λ-S and Ω states were determined, which are in good agreement with the experimental data. The transition dipole moments (TDMs) and the Franck-Condon factors (FCs) of the transitions from the low-lying bound Ω states A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 to the ground state X2Σ+1/2 have also been presented. Based on the previous calculations, the radiative lifetimes of the A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 were evaluated.

  20. EVOLUTION OF IONS AFTER MULTIPLE ELECTRON-CAPTURE FROM SURFACES

    NARCIS (Netherlands)

    MORGENSTERN, R; DAS, J

    1993-01-01

    A comparison is made of the electronic processes which occur when a multiply charged ion is approaching an atomic target on the one hand or a metal surface on the other hand. In both caws three collision phases can be identified: those of attraction, of electron capture and of decay in the vacuum; i

  1. Flexible barrier film, method of forming same, and organic electronic device including same

    Science.gov (United States)

    Blizzard, John; Tonge, James Steven; Weidner, William Kenneth

    2013-03-26

    A flexible barrier film has a thickness of from greater than zero to less than 5,000 nanometers and a water vapor transmission rate of no more than 1.times.10.sup.-2 g/m.sup.2/day at 22.degree. C. and 47% relative humidity. The flexible barrier film is formed from a composition, which comprises a multi-functional acrylate. The composition further comprises the reaction product of an alkoxy-functional organometallic compound and an alkoxy-functional organosilicon compound. A method of forming the flexible barrier film includes the steps of disposing the composition on a substrate and curing the composition to form the flexible barrier film. The flexible barrier film may be utilized in organic electronic devices.

  2. Analysis of electronic models for solar cells including energy resolved defect densities

    Energy Technology Data Exchange (ETDEWEB)

    Glitzky, Annegret

    2010-07-01

    We introduce an electronic model for solar cells including energy resolved defect densities. The resulting drift-diffusion model corresponds to a generalized van Roosbroeck system with additional source terms coupled with ODEs containing space and energy as parameters for all defect densities. The system has to be considered in heterostructures and with mixed boundary conditions from device simulation. We give a weak formulation of the problem. If the boundary data and the sources are compatible with thermodynamic equilibrium the free energy along solutions decays monotonously. In other cases it may be increasing, but we estimate its growth. We establish boundedness and uniqueness results and prove the existence of a weak solution. This is done by considering a regularized problem, showing its solvability and the boundedness of its solutions independent of the regularization level. (orig.)

  3. A split-step method to include electron-electron collisions via Monte Carlo in multiple rate equation simulations

    Science.gov (United States)

    Huthmacher, Klaus; Molberg, Andreas K.; Rethfeld, Bärbel; Gulley, Jeremy R.

    2016-10-01

    A split-step numerical method for calculating ultrafast free-electron dynamics in dielectrics is introduced. The two split steps, independently programmed in C++11 and FORTRAN 2003, are interfaced via the presented open source wrapper. The first step solves a deterministic extended multi-rate equation for the ionization, electron-phonon collisions, and single photon absorption by free-carriers. The second step is stochastic and models electron-electron collisions using Monte-Carlo techniques. This combination of deterministic and stochastic approaches is a unique and efficient method of calculating the nonlinear dynamics of 3D materials exposed to high intensity ultrashort pulses. Results from simulations solving the proposed model demonstrate how electron-electron scattering relaxes the non-equilibrium electron distribution on the femtosecond time scale.

  4. Dynamics of electron in a surface quantum well

    Institute of Scientific and Technical Information of China (English)

    Wang Li-Fei; Yang Guang-Can

    2009-01-01

    This paper studies the quantum dynamics of electrons in a surface quantum well in the time domain with autocorrelation of wave packet. The evolution of the wave packet for different manifold eigenstates with finite and infinite lifetimes is investigated analytically. It is found that the quantum coherence and evolution of the surface electronic wave packet can be controlled by the laser central energy and electric field. The results show that the finite lifetime of excited states expedites the dephasing of the coherent electronic wave packet significantly. The correspondence between classical and quantum mechanics is shown explicitly in the system.

  5. Electronic stimulators for surface neural prosthesis

    Directory of Open Access Journals (Sweden)

    Broderick Barry J.

    2008-01-01

    Full Text Available This paper presents the technological advancements in neural prosthesis devices using Functional Electrical Stimulation (FES. FES refers to the restoration of motor functions lost due to spinal cord injury (SCI, stroke, head injury, or diseases such as Cerebral Palsy or Multiple Sclerosis by eliciting muscular contractions through the use of a neuromuscular electrical stimulator device. The field has developed considerably since its inception, with the miniaturisation of circuity, the development of programmable and adaptable stimulators and the enhancement of sensors used to trigger the application of stimulation to suit a variety of FES applications. This paper discusses general FES system design requirements in the context of existing commercial and research FES devices, focusing on surface stimulators for the upper and lower limbs. These devices have demonstrated feasible standing and stepping in a clinical setting with paraplegic patients, improvements in dropped foot syndrome with hemiplegic patients and aided in the restoration of grasping function in patients with upper limb motor dysfunction.

  6. Systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Cooks, Robert Graham; Li, Anyin; Luo, Qingjie

    2017-08-01

    The invention generally relates to systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions. In certain aspects, the invention provides methods that involve providing a metal and a solvent. The methods additionally involve applying voltage to the solvated metal to thereby produce solvent droplets including ions of the metal containing compound, and directing the solvent droplets including the metal ions to a target. In certain embodiments, once at the target, the metal ions can react directly or catalyze reactions.

  7. Systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Cooks, Robert Graham; Li, Anyin; Luo, Qingjie

    2017-01-24

    The invention generally relates to systems and methods for producing metal clusters; functionalized surfaces; and droplets including solvated metal ions. In certain aspects, the invention provides methods that involve providing a metal and a solvent. The methods additionally involve applying voltage to the solvated metal to thereby produce solvent droplets including ions of the metal containing compound, and directing the solvent droplets including the metal ions to a target. In certain embodiments, once at the target, the metal ions can react directly or catalyze reactions.

  8. Diffuse Surface Scattering in the Plasmonic Resonances of Ultra-Low Electron Density Nanospheres

    CERN Document Server

    Monreal, R Carmina; Apell, S Peter

    2015-01-01

    Localized surface plasmon resonances (LSPRs) have recently been identified in extremely diluted electron systems obtained by doping semiconductor quantum dots. Here we investigate the role that different surface effects, namely electronic spill-out and diffuse surface scattering, play in the optical properties of these ultra-low electron density nanosystems. Diffuse scattering originates from imperfections or roughness at a microscopic scale on the surface. Using an electromagnetic theory that describes this mechanism in conjunction with a dielectric function including the quantum size effect, we find that the LSPRs show an oscillatory behavior both in position and width for large particles and a strong blueshift in energy and an increased width for smaller radii, consistent with recent experimental results for photodoped ZnO nanocrystals. We thus show that the commonly ignored process of diffuse surface scattering is a more important mechanism affecting the plasmonic properties of ultra-low electron density ...

  9. Structure of a bacterial cell surface decaheme electron conduit.

    Science.gov (United States)

    Clarke, Thomas A; Edwards, Marcus J; Gates, Andrew J; Hall, Andrea; White, Gaye F; Bradley, Justin; Reardon, Catherine L; Shi, Liang; Beliaev, Alexander S; Marshall, Matthew J; Wang, Zheming; Watmough, Nicholas J; Fredrickson, James K; Zachara, John M; Butt, Julea N; Richardson, David J

    2011-06-07

    Some bacterial species are able to utilize extracellular mineral forms of iron and manganese as respiratory electron acceptors. In Shewanella oneidensis this involves decaheme cytochromes that are located on the bacterial cell surface at the termini of trans-outer-membrane electron transfer conduits. The cell surface cytochromes can potentially play multiple roles in mediating electron transfer directly to insoluble electron sinks, catalyzing electron exchange with flavin electron shuttles or participating in extracellular intercytochrome electron exchange along "nanowire" appendages. We present a 3.2-Å crystal structure of one of these decaheme cytochromes, MtrF, that allows the spatial organization of the 10 hemes to be visualized for the first time. The hemes are organized across four domains in a unique crossed conformation, in which a staggered 65-Å octaheme chain transects the length of the protein and is bisected by a planar 45-Å tetraheme chain that connects two extended Greek key split β-barrel domains. The structure provides molecular insight into how reduction of insoluble substrate (e.g., minerals), soluble substrates (e.g., flavins), and cytochrome redox partners might be possible in tandem at different termini of a trifurcated electron transport chain on the cell surface.

  10. On the modelling of semi-insulating GaAs including surface tension and bulk stresses

    Energy Technology Data Exchange (ETDEWEB)

    Dreyer, W.; Duderstadt, F.

    2004-07-01

    Necessary heat treatment of single crystal semi-insulating Gallium Arsenide (GaAs), which is deployed in micro- and opto- electronic devices, generate undesirable liquid precipitates in the solid phase. The appearance of precipitates is influenced by surface tension at the liquid/solid interface and deviatoric stresses in the solid. The central quantity for the description of the various aspects of phase transitions is the chemical potential, which can be additively decomposed into a chemical and a mechanical part. In particular the calculation of the mechanical part of the chemical potential is of crucial importance. We determine the chemical potential in the framework of the St. Venant-Kirchhoff law which gives an appropriate stress/strain relation for many solids in the small strain regime. We establish criteria, which allow the correct replacement of the St. Venant-Kirchhoff law by the simpler Hooke law. The main objectives of this study are: (i) We develop a thermo-mechanical model that describes diffusion and interface motion, which both are strongly influenced by surface tension effects and deviatoric stresses. (ii) We give an overview and outlook on problems that can be posed and solved within the framework of the model. (iii) We calculate non-standard phase diagrams, i.e. those that take into account surface tension and non-deviatoric stresses, for GaAs above 786 C, and we compare the results with classical phase diagrams without these phenomena. (orig.)

  11. Plasmonics—the interaction of light with metal surface electrons

    Science.gov (United States)

    Kroó, Norbert; Rácz, Péter

    2016-08-01

    The realization of light amplification by stimulated emission of radiation opened up an enormous wealth of potential new research and technologies in a broad wavelength range of electromagnetic waves. One of the new fields is plasmonics, based on the special properties of some materials with negative refractive index. In this case surface electromagnetic waves, coupled to surface electrons, the so-called surface plasmons can be generated. These waves among others represent a large enhancement of the EM field near the surface of the materials. The present paper illustrates some of the consequences of this phenomenon for a broad range of phenomena from ‘lasing’ to electron pairing. The latter is the basic condition for superconductivity, in our case found at room temperature. Measurements with a scanning tunneling microscope, furthermore electron and photon emission studies are the source of the presented experimental data.

  12. Biophysical insights into how surfaces, including lipid membranes, modulate protein aggregation related to neurodegeneration

    Directory of Open Access Journals (Sweden)

    Kathleen A Burke

    2013-03-01

    Full Text Available There are a vast number of neurodegenerative diseases, including Alzheimer’s disease (AD, Parkinson’s disease (PD, and Huntington’s disease (HD, associated with the rearrangement of specific proteins to non-native conformations that promotes aggregation and deposition within tissues and/or cellular compartments. These diseases are commonly classified as protein misfolding or amyloid diseases. The interaction of these proteins with liquid/surface interfaces is a fundamental phenomenon with potential implications for protein misfolding diseases. Kinetic and thermodynamic studies indicate that significant conformational changes can be induced in proteins encountering surfaces, which can play a critical role in nucleating aggregate formation or stabilizing specific aggregation states. Surfaces of particular interest in neurodegenerative diseases are cellular and subcellular membranes that are predominately comprised of lipid components. The two-dimensional liquid environments provided by lipid bilayers can profoundly alter protein structure and dynamics by both specific and nonspecific interactions. Importantly for misfolding diseases, these bilayer properties can not only modulate protein conformation, but also exert influence on aggregation state. A detailed understanding of the influence of (subcellular surfaces in driving protein aggregation and/or stabilizing specific aggregate forms could provide new insights into toxic mechanisms associated with these diseases. Here, we review the influence of surfaces in driving and stabilizing protein aggregation with a specific emphasis on lipid membranes.

  13. Screened test-charge - electron interaction including many-body effects in two and three dimensions

    Science.gov (United States)

    Gold, A.; Ghazali, A.

    1997-05-01

    Bound states of a negatively charged test particle and an electron are studied by incorporating many-body effects (exchange and correlation) in the screening function of an interacting electron gas via the local-field correction. Using a variational method and a matrix-diagonalization method we determine the energies and the wave functions of the ground state and the excited states as functions of the electron density for three-dimensional and two-dimensional systems. For high electron density no bound states are found. Below a critical density the number and the energy of the bound states increase with decreasing electron density. We also present results for bound-state energies of a positively charged test particle with an electron, and compare them with results obtained within the random-phase approximation where the local-field correction is ignored.

  14. MODIFICATION OF SURFACE LAYERS FOR SILICATE GLASSES BY ELECTRON IRRADIATION

    Directory of Open Access Journals (Sweden)

    V. S. Brunov

    2014-05-01

    Full Text Available Experimental research results of silicate glass surface layers modification by the influence of electron beams with 5-50 keV energies and 20-50 mC/cm2 doses are presented. It is shown that during the glasses exposure to an electron beam with 20-50 keV electron energies, a gradient optical waveguide with increased refractive index on waveguide axis Δn = 0.01-0.04 is formed in the surface layer. Сhemical etching rate is increased in the exposed area by up to two times which is related to glass grid destruction. Depending on irradiation dose thin film or silver nanoparticles with the size less than 20nm are formed on the surface of the silver containing glasses for electron energies less than 10 keV. Silver films drawn on the surface of the glass are dissolved into the glass bulk for electron energies 20-50 keV and 20-50 mC/cm2 dose. Basic mechanisms causing these effects are: chemical bonds breaking of spatial glass grid by high energy electrons, formation of negative volume charge inside the glass and field migration of positive metal ions into the volume charge region. Achieved results can be used in photonics, integral optics and nanoplasmonics device fabrication.

  15. 76 FR 45860 - In the Matter of Certain Electronic Devices, Including Wireless Communication Devices, Portable...

    Science.gov (United States)

    2011-08-01

    ... behalf of Samsung Electronics Co., Ltd. of Korea and Samsung Telecommunications America, LLC of... of investigation shall be served: (a) The complainants are: Samsung Electronics Co., Ltd., 416 Maetan-3dong, Yeongtong-gu, Suwon- City, Gyeonggi-do, Korea 443-742; Samsung Telecommunications America, LLC...

  16. Design of an HHFW antenna including high impedance surfaces for FTU

    Science.gov (United States)

    Milanesio, Daniele; Maggiora, Riccardo

    2013-10-01

    The successful design of an Ion Cyclotron antenna mainly relies on the capability of coupling high power to the plasma (MW), feature that is currently reached by allowing rather high voltages (tens of kV) on the unavoidable unmatched part of the feeding lines. This requirement is often responsible of arcs along the transmission lines and other unwanted phenomena that considerably limit the usage of IC launchers. In this work, we suggest and describe a revolutionary approach based on high impedance surfaces, which allows to increase the antenna radiation efficiency and, hence, to highly reduce the imposed voltages to couple the same level of power to the plasma. High-impedance surfaces are periodic metallic structures (patches) displaced usually on top of a dielectric substrate and grounded by means of vertical posts usually embedded inside the dielectric, in a mushroom-like shape. In terms of working properties, high impedance surfaces are electrically thin in-phase reflectors, i.e. they present a high impedance, within a given frequency band, such that the image currents are in-phase with the currents of the antenna itself, thus determining a significant efficiency increase. This work documents the design by means of numerical codes of an antenna including high impedance surfaces to be tested on the FTU IBW port and fed by the FTU IBW generators at 433 MHz. The test on FTU, if successful, will confirm the possibility to adopt this approach for future HHFW antennas.

  17. Electronic and electrochemical doping of graphene by surface adsorbates

    Directory of Open Access Journals (Sweden)

    Hugo Pinto

    2014-10-01

    Full Text Available Many potential applications of graphene require its precise and controllable doping with charge carriers. Being a two-dimensional material graphene is extremely sensitive to surface adsorbates, so its electronic properties can be effectively modified by deposition of different atoms and molecules. In this paper, we review two mechanisms of graphene doping by surface adsorbates, namely electronic and electrochemical doping. Although, electronic doping has been extensively studied and discussed in the literature, much less attention has been paid to electrochemical doping. This mechanism can, however, explain the doping of graphene by adsorbates for which no charge transfer is expected within the electronic doping model. In addition, electrochemical doping is in the origin of the hysteresis effects often observed in graphene-based field effect transistors when operating in the atmospheric environment.

  18. SIMULATION OF STRONG TURBULENCE FLOW WITH FREE SURFACE INCLUDING THE EFFECTS OF STREAMLINE CURVATURE

    Institute of Scientific and Technical Information of China (English)

    DAI Hui-chao; LIU Yu-ling; WEI Wen-li

    2005-01-01

    This paper is concerned with a mathematical model for two-dimensional strong turbulence flow with free surface including the effects of streamline curvature in orthogonal curvilinear coordinate system, with which the characteristics of the turbulence flow field on the ogee spillway was numerical simulated. In the numerical simulation, the flow control equations in orthogonal curvilinear coordinate system were discretized by the finite volume method, the physical parameters( P, U,V,K,ε,γt,etc.) were arranged on a staggered grid, the discretized equations were solved with the SIMPLEC method, and the complex free surface was dealt with VOF method. The computed results show that the velocity fields, pressure field, shear stress distribution and kinetic energy of turbulent flow on the ogee spillway are in agreement with experimental data. This confirms that the model can be used for numerical simulation of the turbulence flow on ogee spillway.

  19. Enhanced Electron-Phonon Coupling at Metal Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Plummer, Ward E.

    2010-08-04

    The Born-Oppenheimer approximation (BOA) decouples electronic from nuclear motion, providing a focal point for most quantum mechanics textbooks. However, a multitude of important chemical, physical and biological phenomena are driven by violations of this approximation. Vibronic interactions are a necessary ingredient in any process that makes or breaks a covalent bond, for example, conventional catalysis or enzymatically delivered biological reactions. Metastable phenomena associated with defects and dopants in semiconductors, oxides, and glasses entail violation of the BOA. Charge exchange in inorganic polymers, organic slats and biological systems involves charge- induced distortions of the local structure. A classic example is conventional superconductivity, which is driven by the electron-lattice interaction. High-resolution angle-resolved photoemission experiments are yielding new insight into the microscopic origin of electron-phonon coupling (EPC) in anisotropic two-dimensional systems. Our recent surface phonon measurement on the surface of a high-Tc material clearly indicates an important momentum dependent EPC in these materials. In the last few years we have shifted our research focus from solely looking at electron phonon coupling to examining the structure/functionality relationship at the surface of complex transition metal compounds. The investigation on electron phonon coupling has allowed us to move to systems where there is coupling between the lattice, the electrons and the spin.

  20. Surface band-gap narrowing in quantized electron accumulation layers.

    Science.gov (United States)

    King, P D C; Veal, T D; McConville, C F; Zúñiga-Pérez, J; Muñoz-Sanjosé, V; Hopkinson, M; Rienks, E D L; Jensen, M Fuglsang; Hofmann, Ph

    2010-06-25

    An energy gap between the valence and the conduction band is the defining property of a semiconductor, and the gap size plays a crucial role in the design of semiconductor devices. We show that the presence of a two-dimensional electron gas near to the surface of a semiconductor can significantly alter the size of its band gap through many-body effects caused by its high electron density, resulting in a surface band gap that is much smaller than that in the bulk. Apart from reconciling a number of disparate previous experimental findings, the results suggest an entirely new route to spatially inhomogeneous band-gap engineering.

  1. Weissenberg reflection high-energy electron diffraction for surface crystallography.

    Science.gov (United States)

    Abukawa, Tadashi; Yamazaki, Tomoyuki; Yajima, Kentaro; Yoshimura, Koji

    2006-12-15

    The principle of a Weissenberg camera is applied to surface crystallographic analysis by reflection high-energy electron diffraction. By removing inelastic electrons and measuring hundreds of patterns as a function of sample rotation angle phi, kinematical analysis can be performed over a large volume of reciprocal space. The data set is equivalent to a three-dimensional stack of Weissenberg photographs. The method is applied to analysis of an Si(111)-square root of 3 x square root of 3-Ag surface, and the structural data obtained are in excellent agreement with the known atomic structure.

  2. Two-dimensional simulation research of secondary electron emission avalanche discharge on vacuum insulator surface

    Science.gov (United States)

    Cai, Libing; Wang, Jianguo; Zhu, Xiangqin; Wang, Yue; Zhang, Dianhui

    2015-01-01

    Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated outgassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data.

  3. Electron Stimulated Desorption of Condensed Gases on Cryogenic Surfaces

    CERN Document Server

    Tratnik, H; Hilleret, Noël

    2005-01-01

    In ultra-high vacuum systems outgassing from vacuum chamber walls and desorption from surface adsorbates are usually the factors which in°uence pressure and residual gas composition. In particular in beam vacuum systems of accelerators like the LHC, where surfaces are exposed to intense synchro- tron radiation and bombardment by energetic ions and electrons, properties like the molecular desorption yield or secondary electron yield can strongly in°uence the performance of the accelerator. In high-energy particle accelerators operating at liquid helium temperature, cold surfaces are exposed to the bombardment of energetic photons, electrons and ions. The gases released by the subsequent desorption are re-condensed on the cold surfaces and can be re-desorbed by the impinging electrons and ions. The equilibrium coverage reached on the surfaces exposed to the impact of energetic particles depends on the desorption yield of the condensed gases and can a®ect the operation of the accelerator by modifying th...

  4. Electronic structure of disordered alloys, surfaces and interfaces

    CERN Document Server

    Turek, Ilja; Kudrnovský, Josef; Šob, Mojmír; Weinberger, Peter

    1997-01-01

    At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu­ microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela­ tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand­ ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul­ tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use ...

  5. Features of Ion-Electronic Emission from Surface of Semiconductors

    Directory of Open Access Journals (Sweden)

    A. Kurochka

    2013-12-01

    Full Text Available The results of the research value of the current of the secondary electrons in the ion-beam etching of various semiconductors. Shows the setup and electrical circuit of the experiment. An experimental study to determine the dependence of the current of the secondary electrons from the band gap Eg and the height of the potential barrier (electron affinity eχ. It is shown that in the conditions of ion-beam etching of the semiconductor is the penetration of the electric field, which leads to a shift of the energy levels of electrons in the surface layer. Found that the ion-electronic signal emission silicon n-type is higher than the p-type silicon.

  6. Electron Scattering at Surfaces and Interfaces of Transition Metals

    Science.gov (United States)

    Zheng, Pengyuan

    The effect of surfaces on the electron transport at reduced scales is attracting continuous interest due to its broad impact on both the understanding of materials properties and their application for nanoelectronics. The size dependence of for conductor's electrical resistivity rho due to electron surface scattering is most commonly described within the framework of Fuchs and Sondheimer (FS) and their various extensions, which uses a phenomenological scattering parameter p to define the probability of electrons being elastically (i.e. specularly) scattered by the surface without causing an increase of rho at reduced size. However, a basic understanding of what surface chemistry and structure parameters determine the specularity p is still lacking. In addition, the assumption of a spherical Fermi surface in the FS model is too simple for transition metals to give accurate account of the actual surface scattering effect. The goal of this study is to develop an understanding of the physics governing electron surface/interface scattering in transition metals and to study the significance of their Fermi surface shape on surface scattering. The advancement of the scientific knowledge in electron surface and interface scattering of transition metals can provide insights into how to design high-conductivity nanowires that will facilitate the viable development of advanced integrated circuits, thermoelectric power generation and spintronics. Sequential in situ and ex situ transport measurements as a function of surface chemistry demonstrate that electron surface/interface scattering can be engineered by surface doping, causing a decrease in the rho. For instance, the rho of 9.3-nm-thick epitaxial and polycrystalline Cu is reduced by 11--13% when coated with 0.75 nm Ni. This is due to electron surface scattering which exhibits a specularity p = 0.7 for the Cu-vacuum interface that transitions to completely diffuse (p = 0) when exposed to air. In contrast, Ni-coated surfaces

  7. Surface modification of pure titanium by pulsed electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, X.D. [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Laboratoired' Etude des Microstructures et de Mecanique des Materiaux (LEM3), CNRS UMR 7239, Universite Paul Verlaine - Metz, Ile du Saulcy, 57045 Metz (France); Hao, S.Z., E-mail: ebeam@dlut.edu.cn [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Li, X.N. [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Dong, C., E-mail: dong@dlut.edu.cn [Key Laboratory of Materials Modification and School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Grosdidier, T., E-mail: Thierry.grosdidier@univ-metz.fr [Laboratoired' Etude des Microstructures et de Mecanique des Materiaux (LEM3), CNRS UMR 7239, Universite Paul Verlaine - Metz, Ile du Saulcy, 57045 Metz (France)

    2011-04-15

    The microstructure, hardness and corrosion resistance of commercially pure Ti treated by low energy high current pulsed electron beam (LEHCPEB) have been investigated. The thin near-surface melted layer rapidly solidified into {beta} and subsequently transformed into ultrafine {alpha}' martensite. This has led to a drastic improvement of the corrosion properties and a significant increase (more than 60%) in hardness of the top surface.

  8. Positron studies of surfaces, structure and electronic properties of nanocrystals

    OpenAIRE

    Eijt, S. W. H.; Barbiellini, B.; Houtepen, A.J.; Vanmaekelbergh, D.; Mijnarends, P. E.; Bansil, A.

    2007-01-01

    A brief review is given of recent positron studies of metal and semiconductor nanocrystals. The prospects offered by positron annihilation as a sensitive method to access nanocrystal (NC) properties are described and compared with other experimental methods. The tunability of the electronic structure of nanocrystals underlies their great potential for application in many areas. Owing to their large surface-to-volume ratio, the surfaces and interfaces of NCs play a crucial role in determining ...

  9. Electron density and electron temperature measurements in nanosecond pulse discharges over liquid water surface

    Science.gov (United States)

    Simeni Simeni, M.; Roettgen, A.; Petrishchev, V.; Frederickson, K.; Adamovich, I. V.

    2016-12-01

    Time-resolved electron density, electron temperature, and gas temperature in nanosecond pulse discharges in helium and O2-He mixtures near liquid water surface are measured using Thomson/pure rotational Raman scattering, in two different geometries, (a) ‘diffuse filament’ discharge between a spherical high-voltage electrode and a grounded pin electrode placed in a reservoir filled with distilled water, with the tip exposed, and (b) dielectric barrier discharge between the high-voltage electrode and the liquid water surface. A diffuse plasma filament generated between the electrodes in helium during the primary discharge pulse exhibits noticeable constriction during the secondary discharge pulse several hundred ns later. Adding oxygen to the mixture reduces the plasma filament diameter and enhances constriction during the secondary pulse. In the dielectric barrier discharge, diffuse volumetric plasma occupies nearly the entire space between the high voltage electrode and the liquid surface, and extends radially along the surface. In the filament discharge in helium, adding water to the container results in considerable reduction of plasma lifetime compared to the discharge in dry helium, by about an order of magnitude, indicating rapid electron recombination with water cluster ions. Peak electron density during the pulse is also reduced, by about a factor of two, likely due to dissociative attachment to water vapor during the discharge pulse. These trends become more pronounced as oxygen is added to the mixture, which increases net rate of dissociative attachment. Gas temperature during the primary discharge pulse remains near room temperature, after which it increases up to T ~ 500 K over 5 µs and decays back to near room temperature before the next discharge pulse several tens of ms later. As expected, electron density and electron temperature in diffuse DBD plasmas are considerably lower compared to peak values in the filament discharge. Use of Thomson

  10. Peptide-functionalized semiconductor surfaces: strong surface electronic effects from minor alterations to backbone composition.

    Science.gov (United States)

    Matmor, Maayan; Lengyel, George A; Horne, W Seth; Ashkenasy, Nurit

    2017-02-22

    The use of non-canonical amino acids is a powerful way to control protein structure. Here, we show that subtle changes to backbone composition affect the ability of a dipeptide to modify solid surface electronic properties. The extreme sensitivity of the interactions to the peptide structure suggests potential applications in improving the performance of electronic devices.

  11. Extremely confined gap surface-plasmon modes excited by electrons

    DEFF Research Database (Denmark)

    Raza, Søren; Stenger, Nicolas; Pors, Anders Lambertus

    2014-01-01

    High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying...

  12. A micromachined surface stress sensor with electronic readout

    NARCIS (Netherlands)

    Carlen, E.T.; Weinberg, M.S.; Zapata, A.M.; Borenstein, J.T.

    2008-01-01

    A micromachined surface stress sensor has been fabricated and integrated off chip with a low-noise, differential capacitance, electronic readout circuit. The differential capacitance signal is modulated with a high frequency carrier signal, and the output signal is synchronously demodulated and filt

  13. Electron capture by highly charged ions from surfaces and gases

    Energy Technology Data Exchange (ETDEWEB)

    Allen, F.

    2008-01-11

    In this study highly charged ions produced in Electron Beam Ion Traps are used to investigate electron capture from surfaces and gases. The experiments with gas targets focus on spectroscopic measurements of the K-shell x-rays emitted at the end of radiative cascades following electron capture into Rydberg states of Ar{sup 17+} and Ar{sup 18+} ions as a function of collision energy. The ions are extracted from an Electron Beam Ion Trap at an energy of 2 keVu{sup -1}, charge-selected and then decelerated down to 5 eVu{sup -1} for interaction with an argon gas target. For decreasing collision energies a shift to electron capture into low orbital angular momentum capture states is observed. Comparative measurements of the K-shell x-ray emission following electron capture by Ar{sup 17+} and Ar{sup 18+} ions from background gas in the trap are made and a discrepancy in the results compared with those from the extraction experiments is found. Possible explanations are discussed. For the investigation of electron capture from surfaces, highly charged ions are extracted from an Electron Beam Ion Trap at energies of 2 to 3 keVu{sup -1}, charge-selected and directed onto targets comprising arrays of nanoscale apertures in silicon nitride membranes. The highly charged ions implemented are Ar{sup 16+} and Xe{sup 44+} and the aperture targets are formed by focused ion beam drilling in combination with ion beam assisted thin film deposition, achieving hole diameters of 50 to 300 nm and aspect ratios of 1:5 to 3:2. After transport through the nanoscale apertures the ions pass through an electrostatic charge state analyzer and are detected. The percentage of electron capture from the aperture walls is found to be much lower than model predictions and the results are discussed in terms of a capillary guiding mechanism. (orig.)

  14. Transport of fast electrons in a nanowire array with collisional effects included

    Energy Technology Data Exchange (ETDEWEB)

    Li, Boyuan; Zhang, Zhimeng; Wang, Jian; Zhang, Bo; Zhao, Zongqing; Shan, Lianqiang; Zhou, Weimin; Zhang, Baohan [Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, 621900 Mianyang (China); Cao, Lihua [Center for Applied physics and Technology, HEDPs, Peking University, Beijing 100871 (China); Gu, Yuqiu, E-mail: yqgu@caep.ac.cn [Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, 621900 Mianyang (China); Center for Applied physics and Technology, HEDPs, Peking University, Beijing 100871 (China)

    2015-12-15

    The transport of picosecond laser generated fast electrons in a nanowire array is studied with two-dimensional particle-in-cell simulations. Our simulations show that a fast electron beam is initially guided and collimated by strong magnetic filaments in the array. Subsequently, after the decomposition of the structure of nanowire array due to plasma expansion, the beam is still collimated by the resistive magnetic field. An analytical model is established to give a criterion for long-term beam collimation in a nanowire array; it indicates that the nanowire cell should be wide enough to keep the beam collimated in picosecond scale.

  15. Microscopic theory of electron absorption by plasma-facing surfaces

    Science.gov (United States)

    Bronold, F. X.; Fehske, H.

    2017-01-01

    We describe a method for calculating the probability with which the wall of a plasma absorbs an electron at low energy. The method, based on an invariant embedding principle, expresses the electron absorption probability as the probability for transmission through the wall’s long-range surface potential times the probability to stay inside the wall despite of internal backscattering. To illustrate the approach we apply it to a SiO2 surface. Besides emission of optical phonons inside the wall we take elastic scattering at imperfections of the plasma-wall interface into account and obtain absorption probabilities significantly less than unity in accordance with available electron-beam scattering data but in disagreement with the widely used perfect absorber model.

  16. Studies on electronic structure of GaN(0001) surface

    CERN Document Server

    Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K

    2002-01-01

    An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized

  17. Microscopic theory of electron absorption by plasma-facing surfaces

    CERN Document Server

    Bronold, Franz X

    2016-01-01

    We describe a method for calculating the probability with which the wall of a plasma absorbs an electron at low energy. The method, based on an invariant embedding principle, expresses the electron absorption probability as the probability for transmission through the wall's long-range surface potential times the probability to stay inside the wall despite of internal backscattering. To illustrate the approach we apply it to a \\SiOTwo\\ surface. Besides emission of optical phonons inside the wall we take elastic scattering at imperfections of the plasma-wall interface into account and obtain absorption probabilities significantly less than unity in accordance with available electron-beam scattering data but in disagreement with the widely used perfect absorber model.

  18. 78 FR 18457 - Definition of Form I-94 To Include Electronic Format

    Science.gov (United States)

    2013-03-27

    ... Passenger Information System (APIS \\1\\) following 9/11, CBP now collects information on aliens traveling by... DHS will create a Form I-94 in an electronic format based on passenger, passport and visa information... APIS. CBP also now uses the Arrival and Departure Information System (ADIS), which draws information...

  19. Flex Power Grid Lab, an electronic equipment test laboratory for emerging MV applications, including grid inverters

    Energy Technology Data Exchange (ETDEWEB)

    Jong, Erik C.W. de [Flex Power Grid Lab, Arnheim (Netherlands); Vaessen, Peter T.M. [KEMA Nederland B.V., Arnheim (Netherlands)

    2008-07-01

    The success of a sustainable energy supply in a free energy market depends on proper management of the energy flows. For control and management, power electronics are indispensable. The knowledge about electromagnetic power technology and the development of components are about to undergo explosive growth. Due to the emergence of decentralised energy sources and the liberalisation of the energy market, the control and management of electrical flows is gaining in importance. Hierarchically controlled one-way traffic continues to decline in favour of (autonomous) networks supplied by large and small generating stations that provide varying electric currents in all directions within a power grid. The complexity of constantly balancing supply and demand is therefore increasing while the assets are simultaneously being utilised to their limits. Information and communication technology has given power technology a strong impulse. Power electronic technology allows network managers and operators to better guide the energy flow. It therefore also contributes to a more rapid transition to a durable energy supply. For example, the application of power electronics in network-integrated decentralised generators such as micro-CHP, wind turbines and solar cells increases the ability to intervene on an extremely local level in an intelligent manner. This increased application and penetration of grid connected power electronics also inevitably increases the demand for research, knowledge and testing of the behaviour of the equipment when integrated into the grid. (orig.)

  20. Calculation of surface dose in rotational total skin electron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Pla, C.; Heese, R.; Pla, M.; Podgorsak, E.B.

    1984-07-01

    A single-field rotational total skin electron irradiation technique has recently been developed at the McGill University for treatment of skin malignancies. The dose received by a given surface point during rotation in a uniform large electron field depends on the radius of rotation of the surface point, on the local radius of curvature of the contour in the vicinity of the point of interest, and on the shadows cast by limbs (arms upon trunk or head and neck, and legs upon each other). A method for calculating the surface dose distribution on a patient is presented accounting for the various parameters affecting the dose. A series of measurements were performed with polystyrene and a humanoid phantom, and an excellent agreement between measured and calculated dose distributions was obtained.

  1. Secondary electron yield of Cu technical surfaces: Dependence on electron irradiation

    Science.gov (United States)

    Larciprete, R.; Grosso, D. R.; Commisso, M.; Flammini, R.; Cimino, R.

    2013-01-01

    The secondary emission yield (SEY) properties of colaminated Cu samples for LHC beam screens are correlated to the surface chemical composition determined by x-ray photoelectron spectroscopy. The surface of the as-received samples is characterized by the presence of significant quantities of contaminating adsorbates and by the maximum of the SEY curve (δmax⁡) being as high as 2.1. After extended electron scrubbing at kinetic energy of 10 and 500 eV, the δmax⁡ value drops to the ultimate values of 1.35 and 1.1, respectively. In both cases the surface oxidized phases are significantly reduced, whereas only in the sample scrubbed at 500 eV the formation of a graphitic-like C layer is observed. We find that the electron scrubbing of technical Cu surfaces can be described as occurring in two steps: the first step consists in the electron-induced desorption of weakly bound contaminants that occurs indifferently at 10 and at 500 eV and corresponds to a partial decrease of δmax⁡; the second step, activated by more energetic electrons and becoming evident at high doses, increases the number of graphitic-like C-C bonds via the dissociation of adsorbates already contaminating the as-received surface or accumulating on this surface during irradiation. Our results demonstrate how the kinetic energy of impinging electrons is a crucial parameter when conditioning the surfaces of Cu and other metals by means of electron-induced chemical processing.

  2. Visualizing Surface Plasmons with Photons, Photoelectrons, and Electrons

    Energy Technology Data Exchange (ETDEWEB)

    El-Khoury, Patrick Z.; Abellan Baeza, Patricia; Gong, Yu; Hage, F. S.; Cottom, J.; Joly, Alan G.; Brydson, R.; Ramasse, Q. M.; Hess, Wayne P.

    2016-06-21

    Both photons and electrons may be used to excite surface plasmon polaritons, the collective charge density fluctuations at the surface of metal nanostructures. By virtue of their nanoscopic and dissipative nature, a detailed characterization of surface plasmon (SP) eigenmodes in real space-time ultimately requires joint sub-nanometer spatial and sub-femtosecond temporal resolution. The latter realization has driven significant developments in the past few years, aimed at interrogating both localized and propagating SP modes over the relevant length and time scales. In this mini-review, we briefly highlight different techniques we employ to visualize the enhanced electric fields associated with SPs. Specifically, we discuss recent hyperspectral optical microscopy, tip-enhanced Raman nano-spectroscopy, nonlinear photoemission electron microscopy, as well as correlated scanning transmission electron microscopy-electron energy loss spectroscopy measurements targeting prototypical plasmonic nanostructures and constructs. Through selected practical examples, we examine the information content in multidimensional images recorded by taking advantage of each of the aforementioned techniques. In effect, we illustrate how SPs can be visualized at the ultimate limits of space and time.

  3. Electron beam heating effects during environmental scanning electron microscopy imaging of water condensation on superhydrophobic surfaces

    Science.gov (United States)

    Rykaczewski, K.; Scott, J. H. J.; Fedorov, A. G.

    2011-02-01

    Superhydrophobic surfaces (SHSs) show promise as promoters of dropwise condensation. Droplets with diameters below ˜10 μm account for the majority of the heat transferred during dropwise condensation but their growth dynamics on SHS have not been systematically studied. Due to the complex topography of the surface environmental scanning electron microscopy is the preferred method for observing the growth dynamics of droplets in this size regime. By studying electron beam heating effects on condensed water droplets we establish a magnification limit below which the heating effects are negligible and use this insight to study the mechanism of individual drop growth.

  4. Harvesting the loss: surface plasmon-based hot electron photodetection

    Directory of Open Access Journals (Sweden)

    Li Wei

    2016-11-01

    Full Text Available Although the nonradiative decay of surface plasmons was once thought to be only a parasitic process within the plasmonic and metamaterial communities, hot carriers generated from nonradiative plasmon decay offer new opportunities for harnessing absorption loss. Hot carriers can be harnessed for applications ranging from chemical catalysis, photothermal heating, photovoltaics, and photodetection. Here, we present a review on the recent developments concerning photodetection based on hot electrons. The basic principles and recent progress on hot electron photodetectors are summarized. The challenges and potential future directions are also discussed.

  5. Low-energy electron scattering from molecules, biomolecules and surfaces

    CERN Document Server

    Carsky, Petr

    2011-01-01

    Since the turn of the 21st century, the field of electron molecule collisions has undergone a renaissance. The importance of such collisions in applications from radiation chemistry to astrochemistry has flowered, and their role in industrial processes such as plasma technology and lighting are vital to the advancement of next generation devices. Furthermore, the development of the scanning tunneling microscope highlights the role of such collisions in the condensed phase, in surface processing, and in the development of nanotechnology.Low-Energy Electron Scattering from Molecules, Biomolecule

  6. Hybrid (particle in cell-fluid) simulation of ion-acoustic soliton generation including super-thermal and trapped electrons

    Energy Technology Data Exchange (ETDEWEB)

    Nopoush, M.; Abbasi, H. [Faculty of Physics, Amirkabir University of Technology, P. O. Box 15875-4413, Tehran (Iran, Islamic Republic of)

    2011-08-15

    The present paper is devoted to the simulation of the nonlinear disintegration of a localized perturbation into an ion-acoustic soliton in a plasma. Recently, this problem was studied by a simple model [H. Abbasi et al., Plasma Phys. Controlled Fusion 50, 095007 (2008)]. The main assumptions were (i) in the electron velocity distribution function (DF), the ion-acoustic soliton velocity was neglected in comparison to the electron thermal velocity, (ii) on the ion-acoustic evolution time-scale, the electron velocity DF was assumed to be stationary, and (iii) the calculation was restricted to the small amplitude case. In order to generalize the model, one has to consider the evolution of the electron velocity DF for finite amplitudes. For this purpose, a one dimensional electrostatic hybrid code, particle in cell (PIC)-fluid, was designed. It simulates the electrons dynamics by the PIC method and the cold ions dynamics by the fluid equations. The plasma contains a population of super-thermal electrons and, therefore, a Lorentzian (kappa) velocity DF is used to model the high energy tail in the electron velocity DF. Electron trapping is included in the simulation in view of their nonlinear resonant interaction with the localized perturbation. A Gaussian initial perturbation is used to model the localized perturbation. The influence of both the trapped and the super-thermal electrons on this process is studied and compared with the previous model.

  7. Adhesive flexible barrier film, method of forming same, and organic electronic device including same

    Science.gov (United States)

    Blizzard, John Donald; Weidner, William Kenneth

    2013-02-05

    An adhesive flexible barrier film comprises a substrate and a barrier layer disposed on the substrate. The barrier layer is formed from a barrier composition comprising an organosilicon compound. The adhesive flexible barrier film also comprises an adhesive layer disposed on the barrier layer and formed from an adhesive composition. A method of forming the adhesive flexible barrier film comprises the steps of disposing the barrier composition on the substrate to form the barrier layer, disposing the adhesive composition on the barrier layer to form the adhesive layer, and curing the barrier layer and the adhesive layer. The adhesive flexible barrier film may be utilized in organic electronic devices.

  8. Nanocoating of titanium implant surfaces with organic molecules. Polysaccharides including glycosaminoglycans

    DEFF Research Database (Denmark)

    Gurzawska, Katarzyna; Svava, Rikke; Jørgensen, Niklas Rye

    2012-01-01

    and roughness. This influences cell behaviour on the surface such as adhesion, proliferation and differentiation of cells as well as the mineralization of the extracellular matrix at the implant surfaces. The aim of the present systematic review was to describe organic molecules used for surface nanocoating...

  9. Electronic structure of graphene on Ni surfaces with different orientation

    Energy Technology Data Exchange (ETDEWEB)

    Pudikov, D.A., E-mail: gelbry@gmail.com; Zhizhin, E.V.; Rybkin, A.G.; Rybkina, A.A.; Zhukov, Y.M.; Vilkov, O. Yu.; Shikin, A.M.

    2016-08-15

    An experimental study of the graphene, synthesized by propylene cracking on Ni surfaces with different orientation: (100) and (111), using angle-resolved photoemission, has been performed. It has been shown that graphene on Ni(111) had a perfect lateral structure due to consistency of their lattices, whereas graphene/Ni(100) consisted of a lot of domains. For both systems electronic structure was quite similar and demonstrated a strong bonding of graphene to the underlying Ni surface. After Au intercalation the electronic structure of graphene in both systems was shifted to the Fermi level and became linear in the vicinity of the K point of the Brillouin zone. - Highlights: • Graphene on Ni(111) is well-ordered, whereas on Ni(100) – multi-domain. • Graphene on Ni(111) and Ni(100) is strongly bonded with substrate. • Intercalation of Au atoms restores the linearity in dispersion and makes graphene quasi-free on both Ni(100) and Ni(111).

  10. Simulations of runaway electron generation including the hot-tail effect

    Science.gov (United States)

    Nuga, H.; Yagi, M.; Fukuyama, A.

    2017-08-01

    The hot-tail (H-T) effect in disruption of impurity injections is considered. The contribution of the H-T effect to runaway electron (RE) current, which arises from fast thermal quenching, is studied using a two-dimensional Fokker-Planck simulation. It is found that in a high-density plasma the total RE current is reduced owing to the high collisionality. We also found that if the thermal quench is fast enough to invoke the H-T effect, the effect produces more seed REs than when the H-T effect is excluded even in high-density plasmas. In the high-density region ({{n}\\text{e}}˜ {{10}21}~{{\\text{m}}-3} ) with fast thermal quenching, nevertheless the increment of the seed REs due to the H-T effect is generally small (tens of milliamperes) while the increment of the total RE current reached 2 MA owing to the avalanche effect.

  11. Theoretical study of electronic absorptions in aminopyridines - TCNE CT complexes by quantum chemical methods, including solvent.

    Science.gov (United States)

    Mach, Pavel; Juhász, György; Kyseľ, Ondrej

    2013-11-01

    The geometric and electronic structure of donor-acceptor complexes of TCNE with aniline, o-, m- and p- aminopyridines and pyridine has been studied in gas phase and in solution using CC2, TDDFT and CIS methods. Concerning interaction energy between particular donor and TCNE acceptor it is fairly described by both CC2 (MP2) and DFT-D approaches. Transition energies in gas phase calculated by CC2 approach are in good agreement with available experimental data for aniline. TDDFT calculations with LC-BLYP functional (with standard value of range separation factor μ = 0.47) gives transition energies too high although not as high as CIS. The red solvent shifts, calculated by PCM model with CIS method are qualitative correct, but error in the range of 0.1-0.2 eV should be expected.

  12. Characteristics of surface sterilization using electron cyclotron resonance plasma

    Science.gov (United States)

    Yonesu, Akira; Hara, Kazufumi; Nishikawa, Tatsuya; Hayashi, Nobuya

    2016-07-01

    The characteristics of surface sterilization using electron cyclotron resonance (ECR) plasma were investigated. High-energy electrons and oxygen radicals were observed in the ECR zone using electric probe and optical emission spectroscopic methods. A biological indicator (BI), Geobacillus stearothermophilus, containing 1 × 106 spores was sterilized in 120 s by exposure to oxygen discharges while maintaining a temperature of approximately 55 °C at the BI installation position. Oxygen radicals and high-energy electrons were found to be the sterilizing species in the ECR region. It was demonstrated that the ECR plasma could be produced in narrow tubes with an inner diameter of 5 mm. Moreover, sterilization tests confirmed that the spores present inside the narrow tube were successfully inactivated by ECR plasma irradiation.

  13. Metal and silicate particles including nanoparticles are present in electronic cigarette cartomizer fluid and aerosol.

    Directory of Open Access Journals (Sweden)

    Monique Williams

    Full Text Available Electronic cigarettes (EC deliver aerosol by heating fluid containing nicotine. Cartomizer EC combine the fluid chamber and heating element in a single unit. Because EC do not burn tobacco, they may be safer than conventional cigarettes. Their use is rapidly increasing worldwide with little prior testing of their aerosol.We tested the hypothesis that EC aerosol contains metals derived from various components in EC.Cartomizer contents and aerosols were analyzed using light and electron microscopy, cytotoxicity testing, x-ray microanalysis, particle counting, and inductively coupled plasma optical emission spectrometry.The filament, a nickel-chromium wire, was coupled to a thicker copper wire coated with silver. The silver coating was sometimes missing. Four tin solder joints attached the wires to each other and coupled the copper/silver wire to the air tube and mouthpiece. All cartomizers had evidence of use before packaging (burn spots on the fibers and electrophoretic movement of fluid in the fibers. Fibers in two cartomizers had green deposits that contained copper. Centrifugation of the fibers produced large pellets containing tin. Tin particles and tin whiskers were identified in cartridge fluid and outer fibers. Cartomizer fluid with tin particles was cytotoxic in assays using human pulmonary fibroblasts. The aerosol contained particles >1 µm comprised of tin, silver, iron, nickel, aluminum, and silicate and nanoparticles (<100 nm of tin, chromium and nickel. The concentrations of nine of eleven elements in EC aerosol were higher than or equal to the corresponding concentrations in conventional cigarette smoke. Many of the elements identified in EC aerosol are known to cause respiratory distress and disease.The presence of metal and silicate particles in cartomizer aerosol demonstrates the need for improved quality control in EC design and manufacture and studies on how EC aerosol impacts the health of users and bystanders.

  14. Microscopic theory of the residual surface resistivity of Rashba electrons

    Science.gov (United States)

    Bouaziz, Juba; Lounis, Samir; Blügel, Stefan; Ishida, Hiroshi

    2016-07-01

    A microscopic expression of the residual electrical resistivity tensor is derived in linear response theory for Rashba electrons scattering at a magnetic impurity with cylindrical or noncylindrical potential. The behavior of the longitudinal and transversal residual resistivity is obtained analytically and computed for an Fe impurity at the Au(111) surface. We studied the evolution of the resistivity tensor elements as a function of the Rashba spin-orbit strength and the magnetization direction of the impurity. We found that the absolute values of longitudinal resistivity reduce with increasing spin-orbit strength of the substrate and that the scattering of the conduction electrons at magnetic impurities with magnetic moments pointing in directions not perpendicular to the surface plane produce a planar Hall effect and an anisotropic magnetoresistance even if the impurity carries no spin-orbit interaction. Functional forms are provided describing the anisotropy of the planar Hall effect and the anisotropic magnetoresistance with respect to the direction of the impurity moment. In the limit of no spin-orbit interaction and a nonmagnetic impurity of cylindrical symmetry, the expression of the residual resistivity of a two-dimensional electron gas has the same simplicity and form as for the three-dimensional electron gas [J. Friedel, J. Nuovo. Cim. 7, 287 (1958), 10.1007/BF02751483] and can also be expressed in terms of scattering phase shifts.

  15. Electron acceleration and high harmonic generation by relativistic surface plasmons

    Science.gov (United States)

    Cantono, Giada; Luca Fedeli Team; Andrea Sgattoni Team; Andrea Macchi Team; Tiberio Ceccotti Team

    2016-10-01

    Intense, short laser pulses with ultra-high contrast allow resonant surface plasmons (SPs) excitation on solid wavelength-scale grating targets, opening the way to the extension of Plasmonics in the relativistic regime and the manipulation of intense electromagnetic fields to develop new short, energetic, laser-synchronized radiation sources. Recent theoretical and experimental studies have explored the role of SP excitation in increasing the laser-target coupling and enhancing ion acceleration, high-order harmonic generation and surface electron acceleration. Here we present our results on SP driven electron acceleration from grating targets at ultra-high laser intensities (I = 5 ×1019 W/cm2, τ = 25 fs). When the resonant condition for SP excitation is fulfilled, electrons are emitted in a narrow cone along the target surface, with a total charge of about 100 pC and energy spectra peaked around 5 MeV. Distinguishing features of the resonant process were investigated by varying the incidence angle, grating type and with the support of 3D PIC simulations, which closely reproduced the experimental data. Open challenges and further measurements on high-order harmonic generation in presence of a relativistic SP will also be discussed.

  16. Electronic structure tuning via surface modification in semimetallic nanowires

    Science.gov (United States)

    Sanchez-Soares, Alfonso; O'Donnell, Conor; Greer, James C.

    2016-12-01

    Electronic structure properties of nanowires (NWs) with diameters of 1.5 and 3 nm based on semimetallic α -Sn are investigated by employing density functional theory and perturbative GW methods. We explore the dependence of electron affinity, band structure, and band-gap values with crystallographic orientation, NW cross-sectional size, and surface passivants of varying electronegativity. We consider four chemical terminations in our study: methyl (CH3), hydrogen (H ), hydroxyl (OH ), and fluorine (F ). Results suggest a high degree of elasticity of Sn-Sn bonds within the Sn NWs' cores with no significant structural variations for nanowires with different surface passivants. Direct band gaps at Brillouin-zone centers are found for most studied structures with quasiparticle corrected band-gap magnitudes ranging from 0.25 to 3.54 eV in 1.5-nm-diameter structures, indicating an exceptional range of properties for semimetal NWs below the semimetal-to-semiconductor transition. Band-gap variations induced by changes in surface passivants indicate the possibility of realizing semimetal-semiconductor interfaces in NWs with constant cross-section and crystallographic orientation, allowing the design of novel dopant-free NW-based electronic devices.

  17. Electron emission from MOS electron emitters with clean and cesium covered gold surface

    DEFF Research Database (Denmark)

    Nielsen, Gunver; Thomsen, Lasse Bjørchmar; Johansson, Martin;

    2009-01-01

    MOS (metal-oxide-semiconductor) electron emitters consisting of a Si substrate, a SiO2 tunnel barrier and a Ti (1 nm)/Au(7 nm) top-electrode, with an active area of 1 cm(2) have been produced and studied with surface science techniques under UHV (ultra high vacuum) conditions and their emission c...

  18. Wet-electron Enhanced Surface Dissociative Electron Attachment Chemistry of Halocarbons

    Science.gov (United States)

    2011-03-14

    photocatalysis , TiO2, decontamination, electron spectroscopy Hrvoje Petek, Xuefeng Cui, Chungwei Lin, and Jin Zhao University of Pittsburgh 123 University...reduction processes on TiO2 surfaces. Therefore it is relevant to the mechanism of photocatalytic decontamination with TiO2 photocatalysis . (a... photocatalysis  with H2O and CH3OH  overlayers.    For a clean TiO2 surface at 90 K O2 molecules do not adsorb on  stoichiometric TiO2 surfaces; they

  19. 75 FR 10502 - In the Matter of Certain Electronic Devices, Including Handheld Wireless Communications Devices...

    Science.gov (United States)

    2010-03-08

    ... investigation named various respondents, including Nokia Corporation of Espoo, Finland and Nokia Inc. of Irving, Texas (collectively ``Nokia''); High Tech Computer Corp. of Taoyuan, Taiwan and HTC America, Inc. of..., 2009, the Commission determined not to review an ID granting a joint motion filed by Saxon and Nokia...

  20. CONFERENCE SUMMARY: Summary and comment on superconducting analogue electronics research, including materials and fabrication, as presented at ISEC 07

    Science.gov (United States)

    Foley, C. P.

    2007-11-01

    The main theme at ISEC 2007 for superconducting materials, fabrication and analogue electronics was the description of incremental developments, including a few new directions that indicate breakthroughs in this area of research. The work on applications focused on their cost-benefit analysis (in order to improve their appeal), the development of simpler systems, making more of the data collected, improving packaging and being responsive to the power handling requirements for commercial systems. All papers presenting this level of research highlighted the importance of obtaining all the necessary details in order to investigate analogue devices and the effectiveness and commercial viability of their systems. This stage of development is important if we are to achieve the transition of superconducting electronics from the laboratory to commercial use. There were some exciting disruptive breakthroughs reported. These were in the areas of nano-SQUIDs, rotating gradiometers, superconducting scanning tunnelling microscopy (Hayashi et al) and the potential of superconducting photonics using optical interfaces with superconducting vortex flow transistors, for example. The materials research in low (LTS), high (HTS) and medium (MTS) critical temperature superconductors was reported. In LTS, nitrides emerged as important materials for use as new tunnel barriers, either insulating or semiconducting. Papers on BaN, NbN, TaN, GaN and Nb-Si superconducting materials were also presented. The MTS material of MgB2 is still under development (Zhao et al). There were also new research groups from South Africa and Turkey attending the conference. The fabrication research presented covered the areas of critical current Ic spread, which is still an issue in reducing the reproducibility of Josephson junctions, a 150 mm process for Nb/Al-AlOx/Nb and methods to improve barrier layers using both new materials and smooth surfaces at thin film interfaces (Du et al). New methods to make sub

  1. Surface spin-electron acoustic waves in magnetically ordered metals

    CERN Document Server

    Andreev, Pavel A

    2015-01-01

    Degenerate plasmas with motionless ions show existence of three surface waves: the Langmuir wave, the electromagnetic wave, and the zeroth sound. Applying the separated spin evolution quantum hydrodynamics to half-space plasma we demonstrate the existence of the surface spin-electron acoustic wave (SSEAW). We study dispersion of the SSEAW. We show that there is hybridization between the surface Langmuir wave and the SSEAW at rather small spin polarization. In the hybridization area the dispersion branches are located close to each other. In this area there is a strong interaction between these waves leading to the energy exchange. Consequently, generating the Langmuir waves with the frequencies close to hybridization area we can generate the SSEAWs. Thus, we report a method of creation of the SEAWs.

  2. Electron backscatter diffraction characterization of laser-induced periodic surface structures on nickel surface

    Energy Technology Data Exchange (ETDEWEB)

    Sedao, Xxx, E-mail: sedao.xxx@gmail.com [Laboratoire Hubert Curien, Université Jean Monnet, 42000 St-Etienne (France); Maurice, Claire [Laboratoire Georges Friedel, Ecole Nationale Supérieure des Mines, 42023 St-Etienne (France); Garrelie, Florence; Colombier, Jean-Philippe; Reynaud, Stéphanie [Laboratoire Hubert Curien, Université Jean Monnet, 42000 St-Etienne (France); Quey, Romain; Blanc, Gilles [Laboratoire Georges Friedel, Ecole Nationale Supérieure des Mines, 42023 St-Etienne (France); Pigeon, Florent [Laboratoire Hubert Curien, Université Jean Monnet, 42000 St-Etienne (France)

    2014-05-01

    Graphical abstract: -- Highlight: •Lattice rotation and its distribution in laser-induced periodic surface structures (LIPSS) and the subsurface region on a nickel substrate are revealed using electron backscatter diffraction (EBSD). -- Abstract: We report on the structural investigation of laser-induced periodic surface structures (LIPSS) generated in polycrystalline nickel target after multi-shot irradiation by femtosecond laser pulses. Electron backscatter diffraction (EBSD) is used to reveal lattice rotation caused by dislocation storage during LIPSS formation. Localized crystallographic damages in the LIPSS are detected from both surface and cross-sectional EBSD studies. A surface region (up to 200 nm) with 1–3° grain disorientation is observed in localized areas from the cross-section of the LIPSS. The distribution of the local disorientation is inhomogeneous across the LIPSS and the subsurface region.

  3. Electronic properties of semiconductor surfaces and metal/semiconductor interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Tallarida, M.

    2005-05-15

    This thesis reports investigations of the electronic properties of a semiconductor surface (silicon carbide), a reactive metal/semiconductor interface (manganese/silicon) and a non-reactive metal/semiconductor interface (aluminum-magnesium alloy/silicon). The (2 x 1) reconstruction of the 6H-SiC(0001) surface has been obtained by cleaving the sample along the (0001) direction. This reconstruction has not been observed up to now for this compound, and has been compared with those of similar elemental semiconductors of the fourth group of the periodic table. This comparison has been carried out by making use of photoemission spectroscopy, analyzing the core level shifts of both Si 2p and C 1s core levels in terms of charge transfer between atoms of both elements and in different chemical environments. From this comparison, a difference between the reconstruction on the Si-terminated and the C-terminated surface was established, due to the ionic nature of the Si-C bond. The growth of manganese films on Si(111) in the 1-5 ML thickness range has been studied by means of LEED, STM and photoemission spectroscopy. By the complementary use of these surface science techniques, two different phases have been observed for two thickness regimes (<1 ML and >1 ML), which exhibit a different electronic character. The two reconstructions, the (1 x 1)-phase and the ({radical}3 x {radical}3)R30 -phase, are due to silicide formation, as observed in core level spectroscopy. The growth proceeds via island formation in the monolayer regime, while the thicker films show flat layers interrupted by deep holes. On the basis of STM investigations, this growth mode has been attributed to strain due to lattice mismatch between the substrate and the silicide. Co-deposition of Al and Mg onto a Si(111) substrate at low temperature (100K) resulted in the formation of thin alloy films. By varying the relative content of both elements, the thin films exhibited different electronic properties

  4. Surface-wave mode coupling : modelling and inverting waveforms including body-wave phases

    NARCIS (Netherlands)

    Marquering, H.A.

    1996-01-01

    This thesis is concerned with a similar problem as addressed by Li & Tanimoto (1993) in the surfacewave mode approach. In this thesis it is shown that surface-wave mode coupling is required when body-wave phases in laterally heterogeneous media are modelled by surface-wave mode summation. An efficie

  5. Zeeman shift of an electron trapped near a surface

    Science.gov (United States)

    Bennett, Robert; Eberlein, Claudia

    2014-04-01

    Boundary-dependent corrections to the spin energy eigenvalues of an electron in a weak magnetic field and confined by a harmonic trapping potential are investigated. The electromagnetic field is quantized through a normal-mode expansion obeying the Maxwell boundary conditions at the material surface. We couple the electron to this photon field and a classical magnetic field in the Dirac equation, to which we apply the unitary Foldy-Wouthuysen transformation in order to generate a nonrelativistic approximation of the Hamiltonian to the desired order. We obtain the Schrödinger eigenstates of an electron subject to double confinement by a harmonic potential and a classical magnetic field, and then use these within second-order perturbation theory to calculate the spin energy shift that is attributable to the surface-modified quantized field. We find that a pole at the eigenfrequency of a set of generalized Landau transitions gives dominant oscillatory contributions to the energy shift in the limit of tight harmonic confinement in a weak magnetic field, which also make the energy shift preferable to the magnetic moment for a physically meaningful interpretation.

  6. Multiscale approach to the electronic structure of doped semiconductor surfaces

    Science.gov (United States)

    Sinai, Ofer; Hofmann, Oliver T.; Rinke, Patrick; Scheffler, Matthias; Heimel, Georg; Kronik, Leeor

    2015-02-01

    The inclusion of the global effects of semiconductor doping poses a unique challenge for first-principles simulations, because the typically low concentration of dopants renders an explicit treatment intractable. Furthermore, the width of the space-charge region (SCR) at charged surfaces often exceeds realistic supercell dimensions. Here, we present a multiscale technique that fully addresses these difficulties. It is based on the introduction of a charged sheet, mimicking the SCR-related field, along with free charge which mimics the bulk charge reservoir, such that the system is neutral overall. These augment a slab comprising "pseudoatoms" possessing a fractional nuclear charge matching the bulk doping concentration. Self-consistency is reached by imposing charge conservation and Fermi level equilibration between the bulk, treated semiclassically, and the electronic states of the slab, which are treated quantum-mechanically. The method, called CREST—the charge-reservoir electrostatic sheet technique—can be used with standard electronic structure codes. We validate CREST using a simple tight-binding model, which allows for comparison of its results with calculations encompassing the full SCR explicitly. Specifically, we show that CREST successfully predicts scenarios spanning the range from no to full Fermi level pinning. We then employ it with density functional theory, obtaining insight into the doping dependence of the electronic structures of the metallic "clean-cleaved" Si(111) surface and its semiconducting (2 ×1 ) reconstructions.

  7. Derivation of a viscous KP including surface tension, and related equations

    CERN Document Server

    Meur, Hervé Le

    2015-01-01

    The aim of this article is to derive surface wave models in the presence of surface tension and viscosity. Using the Navier-Stokes equations with a free surface, flat bottom and surface tension, we derive the viscous 2D Boussinesq system with a weak transverse variation. The assumed transverse variation is on a larger scale than along the main propagation direction. This Boussinesq system is only an intermediate result that enables us to derive the Kadomtsev-Petviashvili (KP) equation which is a 2D generalization of the KdV equation. In addition, we get the 1D KdV equation, and lastly the Boussinesq equation. All these equations are derived for non-vanishing initial conditions.

  8. Application of Electron Beam Surface Technologies in the Automotive Industry

    Institute of Scientific and Technical Information of China (English)

    Rolf Zenker; Anja Buchwalder

    2004-01-01

    Progress in the beam deflection technique opens up new possibilities for the application of electron beam (EB)surface and welding technologies in the automotive industry. This development is based on three-dimensional high-speed beam deflection and fully automatic online process control. So, in the EB surface treatment three-dimensional energy transfer fields can be realised which take into account the contour of a component, the conditions of heat conduction and the load conditions. High flexibility, precision and reproducibility are typical characteristics. High productivity is achieved by the simultaneous interaction of the EB in several processing areas or by carrying out several processes simultaneously. EB surface treatment is becoming more and more attractive and important especially in the automotive industry, and also in comparison to laser technologies. This paper deals with different EB surface technologies, for example hardening,remelting, surface alloying, dispersing or cladding of different materials such as steel, cast iron and different alloys of Al,Mg and Ti. Examples of applications in the automotive industry, especially engine components, will be discussed.

  9. Electron backscatter diffraction characterization of laser-induced periodic surface structures on nickel surface

    Science.gov (United States)

    Sedao, Xxx; Maurice, Claire; Garrelie, Florence; Colombier, Jean-Philippe; Reynaud, Stéphanie; Quey, Romain; Blanc, Gilles; Pigeon, Florent

    2014-05-01

    We report on the structural investigation of laser-induced periodic surface structures (LIPSS) generated in polycrystalline nickel target after multi-shot irradiation by femtosecond laser pulses. Electron backscatter diffraction (EBSD) is used to reveal lattice rotation caused by dislocation storage during LIPSS formation. Localized crystallographic damages in the LIPSS are detected from both surface and cross-sectional EBSD studies. A surface region (up to 200 nm) with 1-3° grain disorientation is observed in localized areas from the cross-section of the LIPSS. The distribution of the local disorientation is inhomogeneous across the LIPSS and the subsurface region.

  10. Eigenmodes and mode competition in a high-gain free-electron laser including alternating-gradient focusing

    CERN Document Server

    Wu Ju Ha

    2001-01-01

    We solve the eigenvalue problem for a high gain free-electron laser in the 'water-bag' model including alternating-gradient focusing by a variational-solution-based (VSB) expansion method. Such VSB expansion method is very efficient for finding the eigenvalue. The results agree with those obtained by numerical simulation quite well. We further discuss the mode degeneracy and mode competition.

  11. 76 FR 16446 - Delphi Corporation Electronics And Safety Division Including On-Site Leased Workers From Acro...

    Science.gov (United States)

    2011-03-23

    ... Employment and Training Administration Delphi Corporation Electronics And Safety Division Including On- Site... Alternative Trade Adjustment Assistance In accordance with Section 223 of the Trade Act of 1974 (19 U.S.C. 2273), and Section 246 of the Trade Act of 1974 (26 U.S.C. 2813), as amended, the Department of...

  12. Towards an Electronic Dog Nose: Surface Plasmon Resonance Immunosensor for Security and Safety

    Directory of Open Access Journals (Sweden)

    Takeshi Onodera

    2014-09-01

    Full Text Available This review describes an “electronic dog nose” based on a surface plasmon resonance (SPR sensor and an antigen–antibody interaction for security and safety. We have concentrated on developing appropriate sensor surfaces for the SPR sensor for practical use. The review covers different surface fabrications, which all include variations of a self-assembled monolayer containing oligo(ethylene glycol, dendrimer, and hydrophilic polymer. We have carried out detection of explosives using the sensor surfaces. For the SPR sensor to detect explosives, the vapor or particles of the target substances have to be dissolved in a liquid. Therefore, we also review the development of sampling processes for explosives, and a protocol for the measurement of explosives on the SPR sensor in the field. Additionally, sensing elements, which have the potential to be applied for the electronic dog nose, are described.

  13. Nanoscale electron transport at the surface of a topological insulator

    Science.gov (United States)

    Bauer, Sebastian; Bobisch, Christian A.

    2016-01-01

    The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role. PMID:27098939

  14. Nanoscale electron transport at the surface of a topological insulator

    Science.gov (United States)

    Bauer, Sebastian; Bobisch, Christian A.

    2016-04-01

    The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role.

  15. Electronic structure of benzene adsorbed on Ni and Cu surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Weinelt, M.; Nilsson, A.; Wassdahl, N. [Uppsala Univ. (Sweden)] [and others

    1997-04-01

    Benzene has for a long time served as a prototype adsorption system of large molecules. It adsorbs with the molecular plane parallel to the surface. The bonding of benzene to a transition metal is typically viewed to involve the {pi} system. Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the adsorption strength is reflected in the electronic structure of the adsorbate-substrate complex. The authors have used X-ray Emission (XE) and X-ray Absorption (XA) spectroscopies to selectively study the electronic states localized on the adsorbed benzene molecule. Using XES the occupied states can be studies and with XAS the unoccupied states. The authors have used beamline 8.0 and the Swedish endstation equipped with a grazing incidence x-ray spectrometer and a partial yield absorption detector. The resolution in the XES and XAS were 0.5 eV and 0.05 eV, respectively.

  16. Accurate spectroscopic calculations of 21 electronic states of ClO radical including transition properties

    Science.gov (United States)

    Wang, Xinxin; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

    2016-08-01

    The potential energy curves were calculated for the 21 states (X2Π, A2Π, 32Π, 42Π, 52Π, 12Σ+, 22Σ+, 32Σ+, 12Σ-, 22Σ-, 32Σ-, 12Δ, 22Δ, 32Δ, 12Φ, 14Σ+, a4Σ-, 24Σ-, 14Π, 24Π and 14Δ), which originated from the two lowest dissociation channels of ClO radical. The calculations were done for internuclear separations approximately from 0.08 to 1.10 nm using the CASSCF method, which was followed by the icMRCI approach with the aug-cc-pV5Z basis set. Of these 21 states, the 14Π, 24Π, 32Δ, 42Π, 52Π, 12Φ, 32Σ+, 14Δ and 24Σ- states are repulsive. The 12Δ, 12Σ-, 14Σ+, 22Σ-, 12Σ+, 22Σ+, 22Δ and 32Σ- states are very weakly bound. Only the A2Π state has one barrier. The avoided crossing exists between the A2Π and the 32Π state. However, the avoided crossing does not generate any double wells. Core- valence correlation correction was accounted for at the level of an aug-cc-pCVQZ basis set. Scalar relativistic correction was included by the third-order Douglas-Kroll Hamiltonian approximation at the level of an aug-cc-pVQZ basis set. All the potential energy curves were extrapolated to the complete basis set limit. The spectroscopic parameters were determined. The 12Σ-, 22Σ-, 32Σ- and 14Σ+ states may be very difficult to be detected in an experiment, since each of these Λ-S states has only one or two vibrational states. The Franck-Condon factors and radiative lifetimes were calculated for several low vibrational levels of the A2Π - X2Π, 32Π - a4Σ-, 22Δ - a4Σ- and 32Σ- - 12Σ- transitions. The spin-orbit coupling effect on the spectroscopic parameters of the X2Π, A2Π, 32Π, a4Σ- and 22Σ+ states were discussed. The spectroscopic properties reported here can be expected to be reliably predicted ones.

  17. Trapping Surface Electrons on Graphene Layers and Islands

    OpenAIRE

    Niesner, D.; Fauster, Th.; Dadap, J. I.; Zaki, N.; Knox, K. R.; Yeh, P. -C.; Bhandari, R.; Osgood, R. M.; Petrović, M; Kralj, M.

    2011-01-01

    We report the use of time- and angle-resolved two-photon photoemission to map the bound, unoccupied electronic structure of the weakly coupled graphene/Ir(111) system. The energy, dispersion, and lifetime of the lowest three image-potential states are measured. In addition, the weak interaction between Ir and graphene permits observation of resonant transitions from an unquenched Shockley-type surface state of the Ir substrate to graphene/Ir image-potential states. The image-potential-state l...

  18. Global Surface Solar Energy Anomalies Including El Nino and La Nina Years

    Science.gov (United States)

    Whitlock, C. H.; Brown, D. E.; Chandler, W. S.; DiPasquale, R. C.; Ritchey, Nancy A.; Gupta, Shashi K.; Wilber, Anne C.; Kratz, David P.; Stackhouse, Paul W.

    2001-01-01

    This paper synthesizes past events in an attempt to define the general magnitude, duration, and location of large surface solar anomalies over the globe. Surface solar energy values are mostly a function of solar zenith angle, cloud conditions, column atmospheric water vapor, aerosols, and surface albedo. For this study, solar and meteorological parameters for the 10-yr period July 1983 through June 1993 are used. These data were generated as part of the Release 3 Surface meteorology and Solar Energy (SSE) activity under the NASA Earth Science Enterprise (ESE) effort. Release 3 SSE uses upgraded input data and methods relative to previous releases. Cloud conditions are based on recent NASA Version-D International Satellite Cloud Climatology Project (ISCCP) global satellite radiation and cloud data. Meteorological inputs are from Version-I Goddard Earth Observing System (GEOS) reanalysis data that uses both weather station and satellite information. Aerosol transmission for different regions and seasons are for an 'average' year based on historic solar energy data from over 1000 ground sites courtesy of Natural Resources Canada (NRCan). These data are input to a new Langley Parameterized Shortwave Algorithm (LPSA) that calculates surface albedo and surface solar energy. That algorithm is an upgraded version of the 'Staylor' algorithm. Calculations are performed for a 280X280 km equal-area grid system over the globe based on 3-hourly input data. A bi-linear interpolation process is used to estimate data output values on a 1 X 1 degree grid system over the globe. Maximum anomalies are examined relative to El Nino and La Nina events in the tropical Pacific Ocean. Maximum year-to-year anomalies over the globe are provided for a 10-year period. The data may assist in the design of systems with increased reliability. It may also allow for better planning for emergency assistance during some atypical events.

  19. Improvement of carbon fiber surface properties using electron beam irradiation

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Carbon fiber-reinforced advance composites have been used for struetural applications, mainly on account of their mechanical properties. The main factor for a good mechanical performance of carbon fiber-reinforced composite is the interfacial interaction between its components, which are carbon fiber and polymeric matrix. The aim of this study is to improve the surface properties of the carbon fiber using ionizing radiation from an electron beam to obtain better adhesion properties in the resultant composite. EB radiation was applied on the carbon fiber itself before preparing test specimens for the mechanical tests. Experimental results showed that EB irradiation improved the tensile strength of carbon fiber samples. The maximum value in tensile strength was reached using doses of about 250kGy. After breakage, the morphology aspect of the tensile specimens prepared with irradiated and non-irradiated carbon fibers were evaluated. SEM micrographs showed modifications on the carbon fiber surface.

  20. Surface Science Analysis of GaAs Photocathodes Following Sustained Electron Beam Delivery

    Energy Technology Data Exchange (ETDEWEB)

    Shutthanandan, V.; Zhu, Zihua; Stutzman, Marcy L.; Hannon, Fay; Hernandez-Garcia, Carlos; Nandasiri, Manjula I.; Kuchibhatla, Satyanarayana V N T; Thevuthasan, Suntharampillai; Hess, Wayne P.

    2012-06-12

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Several photocathode degradation processes are suspected, including defect formation by ion back bombardment, photochemistry of surface adsorbed species and irradiation-induced surface defect formation. To better understand the mechanisms of photocathode degradation, we have conducted surface and bulk analysis studies of two GaAs photocathodes removed from the FEL photoinjector after delivering electron beam for a few years. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, strained super-lattice GaAs photocathode samples, removed from the CEBAF photoinjector were analyzed using Transmission Electron Microscopy (TEM) and SIMS. This analysis of photocathode degradation during nominal photoinjector operating conditions represents first steps towards developing robust new photocathode designs necessary for generating sub-micron emittance electron beams required for both fourth generation light sources and intense polarized CW electron beams for nuclear and high energy physics facilities.

  1. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Energy Technology Data Exchange (ETDEWEB)

    Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  2. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Directory of Open Access Journals (Sweden)

    V. Shutthanandan

    2012-06-01

    Full Text Available Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL. Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS, atomic force microscopy, and secondary ion mass spectrometry (SIMS. In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  3. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Energy Technology Data Exchange (ETDEWEB)

    Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  4. Surface wave site characterization at 27 locations near Boston, Massachusetts, including 2 strong-motion stations

    Science.gov (United States)

    Thompson, Eric M.; Carkin, Bradley A.; Baise, Laurie G.; Kayen, Robert E.

    2014-01-01

    The geotechnical properties of the soils in and around Boston, Massachusetts, have been extensively studied. This is partly due to the importance of the Boston Blue Clay and the extent of landfill in the Boston area. Although New England is not a region that is typically associated with seismic hazards, there have been several historical earthquakes that have caused significant ground shaking (for example, see Street and Lacroix, 1979; Ebel, 1996; Ebel, 2006). The possibility of strong ground shaking, along with heightened vulnerability from unreinforced masonry buildings, motivates further investigation of seismic hazards throughout New England. Important studies that are pertinent to seismic hazards in New England include source-parameter studies (Somerville and others, 1987; Boore and others, 2010), wave-propagation studies (Frankel, 1991; Viegas and others, 2010), empirical ground-motion prediction equations (GMPE) for computing ground-motion intensity (Tavakoli and Pezeshk, 2005; Atkinson and Boore, 2006), site-response studies (Hayles and others, 2001; Ebel and Kim, 2006), and liquefaction studies (Brankman and Baise, 2008). The shear-wave velocity (VS) profiles collected for this report are pertinent to the GMPE, site response, and liquefaction aspects of seismic hazards in the greater Boston area. Besides the application of these data for the Boston region, the data may be applicable throughout New England, through correlations with geologic units (similar to Ebel and Kim, 2006) or correlations with topographic slope (Wald and Allen, 2007), because few VS measurements are available in stable tectonic regions.Ebel and Hart (2001) used felt earthquake reports to infer amplification patterns throughout the greater Boston region and noted spatial correspondence with the dominant period and amplification factors obtained from ambient noise (horizontal-to-vertical ratios) by Kummer (1998). Britton (2003) compiled geotechnical borings in the area and produced a

  5. Calculation of Ground State Rotational Populations for Kinetic Gas Homonuclear Diatomic Molecules including Electron-Impact Excitation and Wall Collisions

    Energy Technology Data Exchange (ETDEWEB)

    David R. Farley

    2010-08-19

    A model has been developed to calculate the ground-state rotational populations of homonuclear diatomic molecules in kinetic gases, including the effects of electron-impact excitation, wall collisions, and gas feed rate. The equations are exact within the accuracy of the cross sections used and of the assumed equilibrating effect of wall collisions. It is found that the inflow of feed gas and equilibrating wall collisions can significantly affect the rotational distribution in competition with non-equilibrating electron-impact effects. The resulting steady-state rotational distributions are generally Boltzmann for N≥3, with a rotational temperature between the wall and feed gas temperatures. The N=0,1,2 rotational level populations depend sensitively on the relative rates of electron-impact excitation versus wall collision and gas feed rates.

  6. Laser-induced electron dynamics including photoionization: A heuristic model within time-dependent configuration interaction theory.

    Science.gov (United States)

    Klinkusch, Stefan; Saalfrank, Peter; Klamroth, Tillmann

    2009-09-21

    We report simulations of laser-pulse driven many-electron dynamics by means of a simple, heuristic extension of the time-dependent configuration interaction singles (TD-CIS) approach. The extension allows for the treatment of ionizing states as nonstationary states with a finite, energy-dependent lifetime to account for above-threshold ionization losses in laser-driven many-electron dynamics. The extended TD-CIS method is applied to the following specific examples: (i) state-to-state transitions in the LiCN molecule which correspond to intramolecular charge transfer, (ii) creation of electronic wave packets in LiCN including wave packet analysis by pump-probe spectroscopy, and, finally, (iii) the effect of ionization on the dynamic polarizability of H(2) when calculated nonperturbatively by TD-CIS.

  7. Electronic system for floor surface type detection in robotics applications

    Science.gov (United States)

    Tarapata, Grzegorz; Paczesny, Daniel; Tarasiuk, Łukasz

    2016-11-01

    The paper reports a recognizing method base on ultrasonic transducers utilized for the surface types detection. Ultra-sonic signal is transmitted toward the examined substrate, then reflected and scattered signal goes back to another ultra-sonic receiver. Thee measuring signal is generated by a piezo-electric transducer located at specified distance from the tested substrate. The detector is a second piezo-electric transducer located next to the transmitter. Depending on thee type of substrate which is exposed by an ultrasonic wave, the signal is partially absorbed inn the material, diffused and reflected towards the receiver. To measure the level of received signal, the dedicated electronic circuit was design and implemented in the presented systems. Such system was designed too recognize two types of floor surface: solid (like concrete, ceramic stiles, wood) and soft (carpets, floor coverings). The method will be applied in electronic detection system dedicated to autonomous cleaning robots due to selection of appropriate cleaning method. This work presents the concept of ultrasonic signals utilization, the design of both the measurement system and the measuring stand and as well number of wide tests results which validates correctness of applied ultrasonic method.

  8. Mapping Carrier Dynamics on Material Surfaces in Space and Time using Scanning Ultrafast Electron Microscopy

    KAUST Repository

    Sun, Jingya

    2016-02-25

    Selectively capturing the ultrafast dynamics of charge carriers on materials surfaces and at interfaces is crucial to the design of solar cells and optoelectronic devices. Despite extensive research efforts over the past few decades, information and understanding about surface-dynamical processes, including carrier trapping and recombination remains extremely limited. A key challenge is to selectively map such dynamic processes, a capability that is hitherto impractical by time-resolved laser techniques, which are limited by the laser’s relatively large penetration depth and consequently they record mainly bulk information. Such surface dynamics can only be mapped in real space and time by applying four-dimensional (4D) scanning ultrafast electron microscopy (S-UEM), which records snapshots of materials surfaces with nanometer spatial and sub-picosecond temporal resolutions. In this method, the secondary electron (SE) signal emitted from the sample’s surface is extremely sensitive to the surface dynamics and is detected in real time. In several unique applications, we spatially and temporally visualize the SE energy gain and loss, the charge carrier dynamics on the surface of InGaN nanowires and CdSe single crystals and its powder film. We also provide the mechanisms for the observed dynamics, which will be the foundation for future potential applications of S-UEM to a wide range of studies on material surfaces and device interfaces.

  9. Emission of correlated electron pairs from Au(111) and Cu(111) surfaces under low-energy electron impact: Contribution of surface states, d-states and spin effects

    Energy Technology Data Exchange (ETDEWEB)

    Samarin, S., E-mail: samar@physics.uwa.edu.au [Centre for Atomic, Molecular and Surface Physics, University of Western Australia, Perth, WA 6009 (Australia); Research Institute of Physics, St. Petersburg University, St. Petersburg (Russian Federation); Artamonov, O.M. [Research Institute of Physics, St. Petersburg University, St. Petersburg (Russian Federation); Guagliardo, P. [Centre for Microscopy, Characterisation and Analysis, UWA, Perth (Australia); Pravica, L. [Centre for Atomic, Molecular and Surface Physics, University of Western Australia, Perth, WA 6009 (Australia); Baraban, A. [Research Institute of Physics, St. Petersburg University, St. Petersburg (Russian Federation); Schumann, F.O. [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle (Germany); Williams, J.F. [Centre for Atomic, Molecular and Surface Physics, University of Western Australia, Perth, WA 6009 (Australia)

    2015-01-15

    Highlights: • Spin-polarized two-electron spectroscopy (e,2e) was applied for studying surface states on Cu(111) and Au(111). • Relative (to d-states) contribution of surface states in the (e,2e) spectrum decreases exponentially when primary electron energy increases from 14 to 30 eV. • Spin asymmetry is readily observed in the spectra of Au(111) whereas in the spectra of Cu(111) the spin effect is negligible. - Abstract: The emission of correlated electron pairs excited from surfaces of Au(111) and Cu(111) by low-energy electrons is measured and analyzed. Energy and momentum conservation allows identification of electron pairs involving excitation of electrons from Shockley surface states and from valence d-states. The relative contributions of surface and d-states to the measured spectra of correlated electron pairs is shown to depend on the primary electron energy and is larger from surface states at relatively small primary energies. The use of a spin-polarized incident electron beam highlights the spin effects in producing an electron pair. Measurements show that spin effects are larger for the pair excitation from the valence d-states than for pairs excited from the surface states.

  10. Graphene surface plasmon polaritons with opposite in-plane electron oscillations along its two surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Huawei; Ruan, Shuangchen, E-mail: scruan@szu.edu.cn; Zhang, Min; Su, Hong; Li, Irene Ling [Shenzhen Key Laboratory of Laser Engineering, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060 (China); Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, Shenzhen University, Shenzhen 518060 (China)

    2015-08-31

    We predict the existence of a surface plasmon polariton (SPP) mode that can be guided by a graphene monolayer, regardless of the sign of the imaginary part of its conductivity. In this mode, in-plane electron oscillations along two surfaces of graphene are of opposite directions, which is very different from conventional SPPs on graphene. Significantly, coating graphene with dielectric films yields a way to guide the SPPs with both sub-wavelength mode widths and ultra-long propagation distances. In particular, the mode characteristics are very sensitive to the chemical potential of graphene, so the graphene-based waveguide can find applications in many optoelectronic devices.

  11. Resistive Memory for Harsh Electronics: Immunity to Surface Effect and High Corrosion Resistance via Surface Modification

    Science.gov (United States)

    Huang, Teng-Han; Yang, Po-Kang; Lien, Der-Hsien; Kang, Chen-Fang; Tsai, Meng-Lin; Chueh, Yu-Lun; He-Hau, Jr.

    2014-03-01

    The tolerance/resistance of the electronic devices to extremely harsh environments is of supreme interest. Surface effects and chemical corrosion adversely affect stability and operation uniformity of metal oxide resistive memories. To achieve the surrounding-independent behavior, the surface modification is introduced into the ZnO memristors via incorporating fluorine to replace the oxygen sites. F-Zn bonds is formed to prevent oxygen chemisorption and ZnO dissolution upon corrosive atmospheric exposure, which effectively improves switching characteristics against harmful surroundings. In addition, the fluorine doping stabilizes the cycling endurance and narrows the distribution of switching parameters. The outcomes provide valuable insights for future nonvolatile memory developments in harsh electronics.

  12. Numerical Modeling of the Surface Fatigue Crack Propagation Including the Closure Effect

    Science.gov (United States)

    Guchinsky, Ruslan; Petinov, Sergei

    2016-01-01

    Presently modeling of surface fatigue crack growth for residual life assessment of structural elements is almost entirely based on application of the Linear Elastic Fracture Mechanics (LEFM). Generally, it is assumed that the crack front does not essentially change its shape, although it is not always confirmed by experiment. Furthermore, LEFM approach cannot be applied when the stress singularity vanishes due to material plasticity, one of the leading factors associated with the material degradation and fracture. Also, evaluation of stress intensity factors meets difficulties associated with changes in the stress state along the crack front circumference. An approach proposed for simulation the evolution of surface cracks based on application of the Strain-life criterion for fatigue failure and of the finite element modeling of damage accumulation. It takes into account the crack closure effect, the nonlinear behavior of damage accumulation and material compliance increasing due to the damage advance. The damage accumulation technique was applied to model the semi-elliptical crack growth from the initial defect in the steel compact specimen. The results of simulation are in good agreement with the published experimental data.

  13. Control of surface charges by radicals as a principle of antistatic polymers protecting electronic circuitry.

    Science.gov (United States)

    Baytekin, H Tarik; Baytekin, Bilge; Hermans, Thomas M; Kowalczyk, Bartlomiej; Grzybowski, Bartosz A

    2013-09-20

    Even minute quantities of electric charge accumulating on polymer surfaces can cause shocks, explosions, and multibillion-dollar losses to electronic circuitry. This paper demonstrates that to remove static electricity, it is not at all necessary to "target" the charges themselves. Instead, the way to discharge a polymer is to remove radicals from its surface. These radicals colocalize with and stabilize the charges; when they are scavenged, the surfaces discharge rapidly. This radical-charge interplay allows for controlling static electricity by doping common polymers with small amounts of radical-scavenging molecules, including the familiar vitamin E. The effectiveness of this approach is demonstrated by rendering common polymers dust-mitigating and also by using them as coatings that prevent the failure of electronic circuitry.

  14. Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator.

    Science.gov (United States)

    Kawasugi, Yoshitaka; Seki, Kazuhiro; Edagawa, Yusuke; Sato, Yoshiaki; Pu, Jiang; Takenobu, Taishi; Yunoki, Seiji; Yamamoto, Hiroshi M; Kato, Reizo

    2016-08-05

    It is widely recognized that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high Tc cuprates. The doping effect, including the electron-hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spectral weight results in the Fermi arc state under hole doping, while a relatively uniform spectral weight results in the emergence of a non-interacting-like Fermi surface (FS) in the electron-doped state. In accordance with the calculations, the experimentally observed Hall coefficients and resistivity anisotropy correspond to the pocket formed by the Fermi arcs under hole doping and to the non-interacting FS under electron doping.

  15. Trajectory Surface-Hopping Dynamics Including Intersystem Crossing in [Ru(bpy)3](2).

    Science.gov (United States)

    Atkins, Andrew J; González, Leticia

    2017-08-17

    Surface-hopping dynamics coupled to linear response TDDFT and explicit nonadiabatic and spin-orbit couplings have been used to model the ultrafast intersystem crossing (ISC) dynamics in [Ru(bpy)3](2+). Simulations using an ensemble of trajectories starting from the singlet metal-to-ligand charge transfer ((1)MLCT) band show that the manifold of (3)MLCT triplet states is first populated from high-lying singlet states within 26 ± 3 fs. ISC competes with an intricate internal conversion relaxation process within the singlet manifold to the lowest singlet state. Normal-mode analysis and principal component analysis, combined with further dynamical simulations where the nuclei are frozen, unequivocally demonstrate that it is not only the high density of states and the large spin-orbit couplings of the system that promote ISC. Instead, geometrical relaxation involving the nitrogen atoms is required to allow for state mixing and efficient triplet population transfer.

  16. Modification of Fluoropolymer Surfaces with Electronically Conductive Polymers

    Science.gov (United States)

    1993-06-01

    CI0 4)3. Polyaniline was synthesized by mixing equal volumes of a solution that was 0.25 M in ammonium persulfate and a solution that was 0.5 M in...31 Conductive polymers, polypyrrole , lithography 16. PRICE CODE 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION...surface. Fortunately, conductive polymers such as polypyrrole adhere quite well to many substrates, including nylon, polycarbonate, cellulosics

  17. Scanning electron microscopy of human cortical bone failure surfaces.

    Science.gov (United States)

    Braidotti, P; Branca, F P; Stagni, L

    1997-02-01

    Undecalcified samples extracted from human femoral shafts are fractured by bending and the fracture surfaces are examined with a scanning electron microscope (SEM). The investigation is performed on both dry and wet (hydrated with a saline solution) specimens. SEM micrographs show patterns in many respects similar to those observed in fractography studies of laminated fiber-reinforced synthetic composites. In particular, dry and wet samples behave like brittle and ductile matrix laminates, respectively. An analysis carried out on the basis of the mechanisms that dominate the fracture process of laminates shows that a reasonable cortical bone model is that of a laminated composite material whose matrix is composed of extracellular noncollagenous calcified proteins, and the reinforcement is constituted by the calcified collagen fiber system.

  18. Chemistry of SOFC Cathode Surfaces: Fundamental Investigation and Tailoring of Electronic Behavior

    Energy Technology Data Exchange (ETDEWEB)

    Yildiz, Bilge; Heski, Clemens

    2013-08-31

    origins of this phenomenon is therefore needed for designing cathode materials with optimal surface chemistry. We quantitatively assessed the elastic and electrostatic interactions of the dopant with the surrounding lattice as the key driving forces for segregation on model perovskite compounds, LnMnO3 (host cation Ln=La, Sm). Our approach combines surface chemical analysis with X-ray photoelectron and Auger electron spectroscopy on model dense thin films, and computational analysis with density functional theory (DFT) calculations and analytical models. Elastic energy differences were systematically induced in the system by varying the radius of the selected dopants (Ca, Sr, Ba) with respect to the host cations (La, Sm) while retaining the same charge state. Electrostatic energy differences were introduced by varying the distribution of charged oxygen and cation vacancies in our models. Varying the oxygen chemical potential in our experiments induced changes in both the elastic energy and electrostatic interactions. Our results quantitatively demonstrate that the mechanism of dopant segregation on perovskite oxides includes both the elastic and electrostatic energy contributions. A smaller size mismatch between the host and dopant cations and a chemically expanded lattice were found to reduce the segregation level of the dopant and to enable more stable cathode surfaces. Ca-doped LaMnO3 was found to have the most stable surface composition with the least cation segregation among the compositions surveyed. The diffusion kinetics of the larger dopants, Ba and Sr, was found to be slower, and can kinetically trap the segregation at reduced temperatures despite the larger elastic energy driving force. Lastly, scanning probe image-contrast showed that the surface chemical heterogeneities made of dopant oxides upon segregation were electronically insulating. The consistency between the results obtained from experiments, DFT calculations and analytical theory in this work

  19. Chemistry of SOFC Cathode Surfaces: Fundamental Investigation and Tailoring of Electronic Behavior

    Energy Technology Data Exchange (ETDEWEB)

    Yildiz, Bilge; Heski, Clemens

    2013-08-31

    origins of this phenomenon is therefore needed for designing cathode materials with optimal surface chemistry. We quantitatively assessed the elastic and electrostatic interactions of the dopant with the surrounding lattice as the key driving forces for segregation on model perovskite compounds, LnMnO3 (host cation Ln=La, Sm). Our approach combines surface chemical analysis with X-ray photoelectron and Auger electron spectroscopy on model dense thin films, and computational analysis with density functional theory (DFT) calculations and analytical models. Elastic energy differences were systematically induced in the system by varying the radius of the selected dopants (Ca, Sr, Ba) with respect to the host cations (La, Sm) while retaining the same charge state. Electrostatic energy differences were introduced by varying the distribution of charged oxygen and cation vacancies in our models. Varying the oxygen chemical potential in our experiments induced changes in both the elastic energy and electrostatic interactions. Our results quantitatively demonstrate that the mechanism of dopant segregation on perovskite oxides includes both the elastic and electrostatic energy contributions. A smaller size mismatch between the host and dopant cations and a chemically expanded lattice were found to reduce the segregation level of the dopant and to enable more stable cathode surfaces. Ca-doped LaMnO3 was found to have the most stable surface composition with the least cation segregation among the compositions surveyed. The diffusion kinetics of the larger dopants, Ba and Sr, was found to be slower, and can kinetically trap the segregation at reduced temperatures despite the larger elastic energy driving force. Lastly, scanning probe image-contrast showed that the surface chemical heterogeneities made of dopant oxides upon segregation were electronically insulating. The consistency between the results obtained from experiments, DFT calculations and analytical theory in this work

  20. Electronic stopping of keV nitrogen ions interacting with a Pt(110) (1 x 2) surface - a tool to characterize electronic surfaces

    NARCIS (Netherlands)

    Robin, A; Postnikov, AV; Heiland, W

    2005-01-01

    Ion channeling is used to investigate the electronic density corrugation at surfaces by analysing the electronic stopping behaviour of ions scattering grazingly off a clean single crystalline Pt(110)(1 x 2) surface. We use the fact that under these conditions the elastic contribution can be separate

  1. Surface trap mediated electronic transport in biofunctionalized silicon nanowires

    Science.gov (United States)

    Puppo, F.; Traversa, F. L.; Di Ventra, M.; De Micheli, G.; Carrara, S.

    2016-08-01

    Silicon nanowires (SiNWs), fabricated via a top-down approach and then functionalized with biological probes, are used for electrically-based sensing of breast tumor markers. The SiNWs, featuring memristive-like behavior in bare conditions, show, in the presence of biomarkers, modified hysteresis and, more importantly, a voltage memory component, namely a voltage gap. The voltage gap is demonstrated to be a novel and powerful parameter of detection thanks to its high-resolution dependence on charges in proximity of the wire. This unique approach of sensing has never been studied and adopted before. Here, we propose a physical model of the surface electronic transport in Schottky barrier SiNW biosensors, aiming at reproducing and understanding the voltage gap based behavior. The implemented model describes well the experimental I-V characteristics of the device. It also links the modification of the voltage gap to the changing concentration of antigens by showing the decrease of this parameter in response to increasing concentrations of the molecules that are detected with femtomolar resolution in real human samples. Both experiments and simulations highlight the predominant role of the dynamic recombination of the nanowire surface states, with the incoming external charges from bio-species, in the appearance and modification of the voltage gap. Finally, thanks to its compactness, and strict correlation with the physics of the nanodevice, this model can be used to describe and predict the I-V characteristics in other nanostructured devices, for different than antibody-based sensing as well as electronic applications.

  2. Electron-hole interaction and optical excitations in solids, surfaces, and polymers

    OpenAIRE

    Louie, S. G.

    2001-01-01

    The optical properties of a variety of materials have been calculated using a recently developed ab initio method based on solving the Bethe-Salpeter equation of the two-particle Green's functions. Relevant self-energy and electron-hole interaction effects are included from first-principles. Results on selected semiconductors, insulators, surfaces, and conjugated polymers are discussed. In many of these systems, excitonic effects are shown to dramatically alter the excitation energies a...

  3. Electron-hole interaction and optical excitations in solids, surfaces, and polymers

    OpenAIRE

    Louie, S. G.

    2001-01-01

    The optical properties of a variety of materials have been calculated using a recently developed ab initio method based on solving the Bethe-Salpeter equation of the two-particle Green's functions. Relevant self-energy and electron-hole interaction effects are included from first-principles. Results on selected semiconductors, insulators, surfaces, and conjugated polymers are discussed. In many of these systems, excitonic effects are shown to dramatically alter the excitation energies a...

  4. Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

    Science.gov (United States)

    SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

  5. The near-surface electron radiation environment of Saturn's moon Mimas

    Science.gov (United States)

    Nordheim, Tom; Hand, Kevin P.; Paranicas, Christopher; Howett, Carly; Hendrix, Amanda R.; Jones, Geraint H.; Coates, Andrew

    2016-10-01

    Introduction: Saturn's inner mid-size moons are exposed to a number of external weathering processes, including charged particle bombardment and UV photolysis, as well as deposition of E ring grains and interplanetary dust. While optical remote sensing observations by several instruments onboard the Cassini spacecraft have revealed a number of weathering patterns across the surfaces of these moons, it is currently not entirely clear which external process is responsible for which observed weathering pattern. Here we focus on Saturn's moon Mimas and model the effect of energetic electron bombardment across its surface. Our results are discussed in the context of previously reported Cassini remote sensing observations of Mimas.Methods: To model the access of energetic electrons to different surface locations we used a guiding center, bounce-averaged approach which has previously been employed for the Jovian and Saturnian moons. The electron spectrum at the orbit of Mimas was implemented according to the fit functions provided by, which are based on averaged measurements from the Cassini Magnetospheric Imaging Instrument (MIMI) Low Energy Magnetospheric Measurement System (LEMMS) at a narrow corridor near the orbit of Mimas (~3.08 Rs) during the period 2004-2013. The interaction of electrons with the surface of Mimas was implemented using the PLANETOCOSMICS code, which is based on the Geant4 toolkit.Results: We predict a lens-shaped electron energy deposition pattern which extends down to ~cm depths at low latitudes near the center of the leading hemisphere. These results are consistent with previous remote sensing observations of a lens-shaped color anomaly [4] as well as a thermal inertia anomaly at this location. At the trailing hemisphere, we predict a similar lens-shaped electron energy deposition pattern, which to date has not been observed by the Cassini optical remote sensing instruments. We suggest that no corresponding lens-shaped weathering pattern has been

  6. Electronic Noses for Composites Surface Contamination Detection in Aerospace Industry.

    Science.gov (United States)

    Vito, Saverio De; Miglietta, Maria Lucia; Massera, Ettore; Fattoruso, Grazia; Formisano, Fabrizio; Polichetti, Tiziana; Salvato, Maria; Alfano, Brigida; Esposito, Elena; Francia, Girolamo Di

    2017-04-02

    The full exploitation of Composite Fiber Reinforced Polymers (CFRP) in so-called green aircrafts design is still limited by the lack of adequate quality assurance procedures for checking the adhesive bonding assembly, especially in load-critical primary structures. In this respect, contamination of the CFRP panel surface is of significant concern since it may severely affect the bonding and the mechanical properties of the joint. During the last years, the authors have developed and tested an electronic nose as a non-destructive tool for pre-bonding surface inspection for contaminants detection, identification and quantification. Several sensors and sampling architectures have been screened in view of the high Technology Readiness Level (TRL) scenarios requirements. Ad-hoc pattern recognition systems have also been devised to ensure a fast and reliable assessment of the contamination status, by combining real time classifiers and the implementation of a suitable rejection option. Results show that e-noses could be used as first line low cost Non Destructive Test (NDT) tool in aerospace CFRP assembly and maintenance scenarios.

  7. Surface plasmon modes of a single silver nanorod: An electron energy loss study

    DEFF Research Database (Denmark)

    Nicoletti, Olivia; Wubs, Martijn; Mortensen, N. Asger;

    2011-01-01

    We present an electron energy loss study using energy filtered TEM of spatially resolved surface plasmon excitations on a silver nanorod of aspect ratio 14.2 resting on a 30 nm thick silicon nitride membrane. Our results show that the excitation is quantized as resonant modes whose intensity maxima...... vary along the nanorod's length and whose wavelength becomes compressed towards the ends of the nanorod. Theoretical calculations modelling the surface plasmon response of the silver nanorodsilicon nitride system show the importance of including retardation and substrate effects in order to describe...

  8. Electric field cancellation on quartz: a Rb adsorbate induced negative electron affinity surface

    CERN Document Server

    Sedlacek, J A; Rittenhouse, S T; Weck, P F; Sadeghpour, H R; Shaffer, J P

    2015-01-01

    We investigate the (0001) surface of single crystal quartz with a submonolayer of Rb adsorbates. Using Rydberg atom electromagnetically induced transparency, we investigate the electric fields resulting from Rb adsorbed on the quartz surface, and measure the activation energy of the Rb adsorbates. We show that the adsorbed Rb induces a negative electron affinity (NEA) on the quartz surface. The NEA surface allows low energy electrons to bind to the surface and cancel the electric field from the Rb adsorbates. Our results are important for integrating Rydberg atoms into hybrid quantum systems and the fundamental study of atom-surface interactions, as well as applications for electrons bound to a 2D surface.

  9. Operation of a novel hot-electron vertical-cavity surface-emitting laser

    Science.gov (United States)

    Balkan, Naci; O'Brien-Davies, Angela; Thoms, A. B.; Potter, Richard J.; Poolton, Nigel; Adams, Michael J.; Masum, J.; Bek, Alpan; Serpenguzel, Ali; Aydinli, Atilla; Roberts, John S.

    1998-07-01

    The hot Electron Light Emission and Lasing in Semiconductor Heterostructures devices (HELLISH-1) is novel surface emitter consisting of a GaAs quantum well, within the depletion region, on the n side of Ga1-xAlxAs p- n junction. It utilizes hot electron transport parallel to the layers and injection of hot electron hole pairs into the quantum well through a combination of mechanisms including tunnelling, thermionic emission and diffusion of `lucky' carriers. Super Radiant HELLISH-1 is an advanced structure incorporating a lower distributed Bragg reflector (DBR). Combined with the finite reflectivity of the upper semiconductor-air interface reflectivity it defines a quasi- resonant cavity enabling emission output from the top surface with a higher spectral purity. The output power has increased by two orders of magnitude and reduced the full width at half maximum (FWHM) to 20 nm. An upper DBR added to the structure defines HELLISH-VCSEL which is currently the first operational hot electron surface emitting laser and lases at room temperature with a 1.5 nm FWHM. In this work we demonstrate and compare the operation of UB-HELLISH-1 and HELLISH-VCSEL using experimental and theoretical reflectivity spectra over an extensive temperature range.

  10. Probing the structural and dynamical properties of liquid water with models including non-local electron correlation

    Energy Technology Data Exchange (ETDEWEB)

    Del Ben, Mauro, E-mail: delben@chem.uzh.ch; Hutter, Jürg, E-mail: hutter@chem.uzh.ch [Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich (Switzerland); VandeVondele, Joost, E-mail: joost.vandevondele@mat.ethz.ch [Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich (Switzerland)

    2015-08-07

    Water is a ubiquitous liquid that displays a wide range of anomalous properties and has a delicate structure that challenges experiment and simulation alike. The various intermolecular interactions that play an important role, such as repulsion, polarization, hydrogen bonding, and van der Waals interactions, are often difficult to reproduce faithfully in atomistic models. Here, electronic structure theories including all these interactions at equal footing, which requires the inclusion of non-local electron correlation, are used to describe structure and dynamics of bulk liquid water. Isobaric-isothermal (NpT) ensemble simulations based on the Random Phase Approximation (RPA) yield excellent density (0.994 g/ml) and fair radial distribution functions, while various other density functional approximations produce scattered results (0.8-1.2 g/ml). Molecular dynamics simulation in the microcanonical (NVE) ensemble based on Møller-Plesset perturbation theory (MP2) yields dynamical properties in the condensed phase, namely, the infrared spectrum and diffusion constant. At the MP2 and RPA levels of theory, ice is correctly predicted to float on water, resolving one of the anomalies as resulting from a delicate balance between van der Waals and hydrogen bonding interactions. For several properties, obtaining quantitative agreement with experiment requires correction for nuclear quantum effects (NQEs), highlighting their importance, for structure, dynamics, and electronic properties. A computed NQE shift of 0.6 eV for the band gap and absorption spectrum illustrates the latter. Giving access to both structure and dynamics of condensed phase systems, non-local electron correlation will increasingly be used to study systems where weak interactions are of paramount importance.

  11. Possible correlation effects of surface state electrons on a solid hydrogen film

    NARCIS (Netherlands)

    Mugele, Friedrich Gunther; Albrecht, Uwe; Leiderer, Paul; Kono, Kimitoshi

    1992-01-01

    We have investigated the transport properties of surface state electrons on thin quench-condensed hydrogen films for various electron densities. The surface state electron mobility showed a continuous dependence on the plasma parameter Gamma in the range from 20 to 130, indicating a strong influence

  12. Relaxation between electrons and surface phonons of a homogeneously photoexcited metal film

    Indian Academy of Sciences (India)

    Navinder Singh

    2004-11-01

    The energy relaxation between the hot degenerate electrons of a homogeneously photoexcited metal film and the surface phonons (phonon wave vectors in two dimensions) is considered under Debye approximation. The state of electrons and phonons is described by equilibrium Fermi and Bose functions with different temperatures. Two cases for electron scattering by the metal surface, namely specular and diffuse scattering, are considered.

  13. Final Report Theoretical Studies of Surface Reactions on Metals and Electronic Materials

    Energy Technology Data Exchange (ETDEWEB)

    Jerry L. Whitten

    2012-04-23

    This proposal describes the proposed renewal of a theoretical research program on the structure and reactivity of molecules adsorbed on transition metal surfaces. A new direction of the work extends investigations to interfaces between solid surfaces, adsorbates and aqueous solutions and includes fundamental work on photoinduced electron transport into chemisorbed species and into solution. The goal is to discover practical ways to reduce water to hydrogen and oxygen using radiation comparable to that available in the solar spectrum. The work relates to two broad subject areas: photocatalytic processes and production of hydrogen from water. The objective is to obtain high quality solutions of the electronic structure of adsorbate-metal-surface-solution systems so as to allow activation barriers to be calculated and reaction mechanisms to be determined. An ab initio embedding formalism provides a route to the required accuracy. New theoretical methods developed during the previous grant period will be implemented in order to solve the large systems involved in this work. Included is the formulation of a correlation operator that is used to treat localized electron distributions such as ionic or regionally localized distributions. The correlation operator which is expressed as a two-particle projector is used in conjunction with configuration interaction.

  14. Final Report Theoretical Studies of Surface Reactions on Metals and Electronic Materials

    Energy Technology Data Exchange (ETDEWEB)

    Jerry L. Whitten

    2012-04-23

    This proposal describes the proposed renewal of a theoretical research program on the structure and reactivity of molecules adsorbed on transition metal surfaces. A new direction of the work extends investigations to interfaces between solid surfaces, adsorbates and aqueous solutions and includes fundamental work on photoinduced electron transport into chemisorbed species and into solution. The goal is to discover practical ways to reduce water to hydrogen and oxygen using radiation comparable to that available in the solar spectrum. The work relates to two broad subject areas: photocatalytic processes and production of hydrogen from water. The objective is to obtain high quality solutions of the electronic structure of adsorbate-metal-surface-solution systems so as to allow activation barriers to be calculated and reaction mechanisms to be determined. An ab initio embedding formalism provides a route to the required accuracy. New theoretical methods developed during the previous grant period will be implemented in order to solve the large systems involved in this work. Included is the formulation of a correlation operator that is used to treat localized electron distributions such as ionic or regionally localized distributions. The correlation operator which is expressed as a two-particle projector is used in conjunction with configuration interaction.

  15. Electronic Structure of the Perylene / Zinc Oxide Interface: A Computational Study of Photoinduced Electron Transfer and Impact of Surface Defects

    KAUST Repository

    Li, Jingrui

    2015-07-29

    The electronic properties of dye-sensitized semiconductor surfaces consisting of pery- lene chromophores chemisorbed on zinc oxide via different spacer-anchor groups, have been studied at the density-functional-theory level. The energy distributions of the donor states and the rates of photoinduced electron transfer from dye to surface are predicted. We evaluate in particular the impact of saturated versus unsaturated aliphatic spacer groups inserted between the perylene chromophore and the semiconductor as well as the influence of surface defects on the electron-injection rates.

  16. Earthing: Health Implications of Reconnecting the Human Body to the Earth's Surface Electrons

    Directory of Open Access Journals (Sweden)

    Gaétan Chevalier

    2012-01-01

    Full Text Available Environmental medicine generally addresses environmental factors with a negative impact on human health. However, emerging scientific research has revealed a surprisingly positive and overlooked environmental factor on health: direct physical contact with the vast supply of electrons on the surface of the Earth. Modern lifestyle separates humans from such contact. The research suggests that this disconnect may be a major contributor to physiological dysfunction and unwellness. Reconnection with the Earth's electrons has been found to promote intriguing physiological changes and subjective reports of well-being. Earthing (or grounding refers to the discovery of benefits—including better sleep and reduced pain—from walking barefoot outside or sitting, working, or sleeping indoors connected to conductive systems that transfer the Earth's electrons from the ground into the body. This paper reviews the earthing research and the potential of earthing as a simple and easily accessed global modality of significant clinical importance.

  17. Expansion Hamiltonian model for a diatomic molecule adsorbed on a surface: Vibrational states of the CO/Cu(100) system including surface vibrations.

    Science.gov (United States)

    Meng, Qingyong; Meyer, Hans-Dieter

    2015-10-28

    Molecular-surface studies are often done by assuming a corrugated, static (i.e., rigid) surface. To be able to investigate the effects that vibrations of surface atoms may have on spectra and cross sections, an expansion Hamiltonian model is proposed on the basis of the recently reported [R. Marquardt et al., J. Chem. Phys. 132, 074108 (2010)] SAP potential energy surface (PES), which was built for the CO/Cu(100) system with a rigid surface. In contrast to other molecule-surface coupling models, such as the modified surface oscillator model, the coupling between the adsorbed molecule and the surface atoms is already included in the present expansion SAP-PES model, in which a Taylor expansion around the equilibrium positions of the surface atoms is performed. To test the quality of the Taylor expansion, a direct model, that is avoiding the expansion, is also studied. The latter, however, requests that there is only one movable surface atom included. On the basis of the present expansion and direct models, the effects of a moving top copper atom (the one to which CO is bound) on the energy levels of a bound CO/Cu(100) system are studied. For this purpose, the multiconfiguration time-dependent Hartree calculations are carried out to obtain the vibrational fundamentals and overtones of the CO/Cu(100) system including a movable top copper atom. In order to interpret the results, a simple model consisting of two coupled harmonic oscillators is introduced. From these calculations, the vibrational levels of the CO/Cu(100) system as function of the frequency of the top copper atom are discussed.

  18. Expansion Hamiltonian model for a diatomic molecule adsorbed on a surface: Vibrational states of the CO/Cu(100) system including surface vibrations

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Qingyong, E-mail: mengqingyong@dicp.ac.cn [State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, 116023 Dalian (China); Meyer, Hans-Dieter, E-mail: hans-dieter.meyer@pci.uni-heidelberg.de [Theoretische Chemie, Physikalisch-Chemisches Institut, Ruprecht-Karls Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg (Germany)

    2015-10-28

    Molecular-surface studies are often done by assuming a corrugated, static (i.e., rigid) surface. To be able to investigate the effects that vibrations of surface atoms may have on spectra and cross sections, an expansion Hamiltonian model is proposed on the basis of the recently reported [R. Marquardt et al., J. Chem. Phys. 132, 074108 (2010)] SAP potential energy surface (PES), which was built for the CO/Cu(100) system with a rigid surface. In contrast to other molecule-surface coupling models, such as the modified surface oscillator model, the coupling between the adsorbed molecule and the surface atoms is already included in the present expansion SAP-PES model, in which a Taylor expansion around the equilibrium positions of the surface atoms is performed. To test the quality of the Taylor expansion, a direct model, that is avoiding the expansion, is also studied. The latter, however, requests that there is only one movable surface atom included. On the basis of the present expansion and direct models, the effects of a moving top copper atom (the one to which CO is bound) on the energy levels of a bound CO/Cu(100) system are studied. For this purpose, the multiconfiguration time-dependent Hartree calculations are carried out to obtain the vibrational fundamentals and overtones of the CO/Cu(100) system including a movable top copper atom. In order to interpret the results, a simple model consisting of two coupled harmonic oscillators is introduced. From these calculations, the vibrational levels of the CO/Cu(100) system as function of the frequency of the top copper atom are discussed.

  19. Surface topology and electronic structure of layered strontium ruthenates

    Energy Technology Data Exchange (ETDEWEB)

    Bienert, Robert; Klinke, Melanie; Waelsch, Michael; Mietke, Sebastian; Matzdorf, Rene [Experimentalphysik II, Universitaet Kassel (Germany); Peng, Jin; Mao, Zhiqiang [Department of Physics, Tulane University, New Orleans (United States)

    2012-07-01

    In complex materials the interplay of properties like crystal structure, electronic structure and magnetism results in very interesting physical phenomena. The Ruddlesden-Popper series of layered Strontium Ruthenates Sr{sub n+1}Ru{sub n}O{sub 3n+1} describes one class of these materials. The double and triple layer systems behave like a Fermi liquid up to the transition temperature of 15 K and 24 K, respectively. In both compounds the local density of states (LDOS) shows a peak within the dip-like feature around the Fermi energy E{sub F}. Using low-temperature (LT) STM and STS we studied the temperature dependence of the LDOS in the range from 4.7 to 35 K. By increasing the temperature the peak within the dip in the LDOS at E{sub F} is only affected by thermal broadening. The surface unit cell of the Strontium Ruthenates exhibits a c(2 x 2) super structure, which is stable from 4.7 K up to room temperature as shown by our atomically resolved LT STM images and room temperature LEED experiments.

  20. Electron surface layer at the interface of a plasma and a dielectric wall

    CERN Document Server

    Heinisch, Rafael L; Fehske, Holger

    2011-01-01

    We study the potential and the charge distribution across the interface of a plasma and a dielectric wall. For this purpose, the charge bound to the wall is modelled as a quasi-stationary electron surface layer which satisfies Poisson's equation and minimizes the grand canonical potential of the wall-thermalized excess electrons constituting the wall charge. Based on an effective model for a graded interface taking into account the image potential and the offset of the conduction band to the potential just outside the dielectric, we specifically calculate the potential and the electron distribution for magnesium oxide, silicon dioxide and sapphire surfaces in contact with a helium discharge. Depending on the electron affinity of the surface, we find two vastly different behaviors. For negative electron affinity, electrons do not penetrate into the wall and an external surface charge is formed in the image potential, while for positive electron affinity, electrons penetrate into the wall and a space charge lay...

  1. Loop-driven graphical unitary group approach to the electron correlation problem, including configuration interaction energy gradients

    Energy Technology Data Exchange (ETDEWEB)

    Brooks, B.R.

    1979-09-01

    The Graphical Unitary Group Approach (GUGA) was cast into an extraordinarily powerful form by restructuring the Hamiltonian in terms of loop types. This restructuring allows the adoption of the loop-driven formulation which illuminates vast numbers of previously unappreciated relationships between otherwise distinct Hamiltonian matrix elements. The theoretical/methodological contributions made here include the development of the loop-driven formula generation algorithm, a solution of the upper walk problem used to develop a loop breakdown algorithm, the restriction of configuration space employed to the multireference interacting space, and the restructuring of the Hamiltonian in terms of loop types. Several other developments are presented and discussed. Among these developments are the use of new segment coefficients, improvements in the loop-driven algorithm, implicit generation of loops wholly within the external space adapted within the framework of the loop-driven methodology, and comparisons of the diagonalization tape method to the direct method. It is also shown how it is possible to implement the GUGA method without the time-consuming full (m/sup 5/) four-index transformation. A particularly promising new direction presented here involves the use of the GUGA methodology to obtain one-electron and two-electron density matrices. Once these are known, analytical gradients (first derivatives) of the CI potential energy are easily obtained. Several test calculations are examined in detail to illustrate the unique features of the method. Also included is a calculation on the asymmetric 2/sup 1/A' state of SO/sub 2/ with 23,613 configurations to demonstrate methods for the diagonalization of very large matrices on a minicomputer. 6 figures, 6 tables.

  2. Enhanced surface acceleration of fast electrons by using sub-wavelength grating targets

    CERN Document Server

    Hu, Guang-yue; Wang, Wen-tao; Wang, Jing-wei; Huang, Lin-gen; Wang, Xin; Xu, Yi; Liu, Jian-sheng; Shen, Bai-fei; Yu, Wei; Li, Ru-xin; Xu, Zhi-zhan

    2010-01-01

    Surface acceleration of fast electrons in intense laser-plasma interaction is improved by using sub-wavelength grating targets. The fast electron beam emitted along the target surface was enhanced by more than three times relative to that by using planar target. The total number of the fast electrons ejected from the front side of target was also increased by about one time. The method to enhance the surface acceleration of fast electron is effective for various targets with sub-wavelength structured surface, and can be applied widely in the cone-guided fast ignition, energetic ion acceleration, plasma device, and other high energy density physics experiments.

  3. Scanning electron microscopic study of the surface of feline gastric epithelium: a simple method of removing the coating material.

    Science.gov (United States)

    Al-Tikriti, M; Henry, R W; Al-Bagdadi, F K; Hoskins, J; Titkemeyer, C

    1986-01-01

    Scanning electron microscopic examination of the gastric surface epithelial cells is often hindered by the presence of a coating material. Several methods for removal of coating material on feline gastric mucosa were utilized. The cleansed tissues were evaluated using the scanning electron microscope to assess damage caused by the use of various cleansing methods to surface epithelial cells. The stretched stomach washed several times, including rubbing the mucosal surface with gloved fingers, yielded the best results with no apparent damage to the surface epithelial cells. Flushing unstretched stomachs with saline only did not adequately remove coating material. Flushing unstretched stomachs with saline while stroking the surface with a cotton tipped applicator stick removed debris but damaged the surface epithelium.

  4. Extracellular Electron Uptake: Among Autotrophs and Mediated by Surfaces

    DEFF Research Database (Denmark)

    Tremblay, Pier-Luc; Angenent, Largus T.; Zhang, Tian

    2017-01-01

    Autotrophic microbes can acquire electrons from solid donors such as steel, other microbial cells, or electrodes. Based on this feature, bioprocesses are being developed for the microbial electrosynthesis (MES) of useful products from the greenhouse gas CO2. Extracellular electron-transfer mechan......Autotrophic microbes can acquire electrons from solid donors such as steel, other microbial cells, or electrodes. Based on this feature, bioprocesses are being developed for the microbial electrosynthesis (MES) of useful products from the greenhouse gas CO2. Extracellular electron...

  5. A Novel Contactless Method for Characterization of Semiconductors: Surface Electron Beam Induced Voltage in Scanning Electron Microscopy

    Institute of Scientific and Technical Information of China (English)

    朱世秋; E.I.RAU; 杨富华; 郑厚植

    2002-01-01

    We present a novel contactless and nondestructive method called the surface electron beam induced voltage (SEBIV) method for characterizing semiconductor materials and devices. The SEBIV method is based on the detection of the surface potential induced by electron beams of scanning electron microscopy (SEM). The core part of the SEBIV detection set-up is a circular metal detector placed above the sample surface. The capacitance between the circular detector and whole surface of the sample is estimated to be about 0.64pf. It is large enough for the detection of the induced surface potential. The irradiation mode of electron beam (e-beam) influences the signal generation. When the e-beam irradiates on the surface of semiconductors continuously, a differential signal is obtained. The real distribution of surface potentials can be obtained when a pulsed e-beam with a fixed frequency is used for irradiation and a lock-in amplifier is employed for detection. The polarity of induced potential depends on the structure of potential barriers and surface states of samples. The contrast of SEBIV images in SEM changes with irradiation time and e-beam intensity.

  6. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, Joel Glenn [Univ. of California, Berkeley, CA (United States)

    2000-05-01

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

  7. Effect of surface mechanical finishes on charging ability of electron irradiated PMMA in a scanning electron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Rondot, Sebastien, E-mail: sebastien.rondot@univ-reims.fr [Groupe de Recherche en Sciences pour l' Ingenieur, EA4301, Faculte des Sciences, BP 1039, 51687 Reims Cedex 2 (France); Jbara, Omar [Groupe de Recherche en Sciences pour l' Ingenieur, EA4301, Faculte des Sciences, BP 1039, 51687 Reims Cedex 2 (France); Fakhfakh, Slim [LaMaCop, Faculte des Sciences de SFAX, Route Soukra Km 3, BP 1171, C.P 3000 Sfax (Tunisia); Belkorissat, Redouane; Patat, Jean Marc [Groupe de Recherche en Sciences pour l' Ingenieur, EA4301, Faculte des Sciences, BP 1039, 51687 Reims Cedex 2 (France)

    2011-10-01

    Charging of Polymethyl Methacrylate insulators (PMMA), in a scanning electron microscope (SEM) is studied owing to a time resolved current method. This method allows the evolution of trapped charge versus time and the charging time constant to be deduced. The effect of surface roughness change on the ability of PMMA to trapped charge is highlighted. The results show that the trapped charge at the steady state decreases when the roughness increases in the micrometer range while the time constant of charging increases with surface roughness. This behaviour is due to the increase of leakage current and/or enhanced secondary electron emission (SEE). On the one hand, surface mechanical finishes allows, the build up charge in insulators submitted to an electron bombardment to be lowered. On the other hand this treatment allows the secondary electron emission to be raised for some specific applications.

  8. Surface modification of the patterned Al6061/SUS304 metal plates using the large electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dong Min; Kim, Jisu; Park, Sung Soo [School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Eonyang-eup, Ulju-gun, Ulsan Metropolitan City 689-798 (Korea, Republic of); Park, Hyung Wook, E-mail: hwpark@unist.ac.kr [School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Eonyang-eup, Ulju-gun, Ulsan Metropolitan City 689-798 (Korea, Republic of); Ki, Hyungson [School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Eonyang-eup, Ulju-gun, Ulsan Metropolitan City 689-798 (Korea, Republic of)

    2012-11-15

    Highlights: Black-Right-Pointing-Pointer We performed the large-electron-beam polishing of the patterned metal plates. Black-Right-Pointing-Pointer We observed its effect on surface hardness, surface roughness, and water repellency. Black-Right-Pointing-Pointer The contact angle for Al6061 and SUS304 increased after the electron-beam irradiation. Black-Right-Pointing-Pointer We observed the microstructure after the electron beam irradiation. - Abstract: Polishing is a finishing process used to improve surface integrity by reducing surface roughness and residual stress caused by other machining processes. The recently developed electron beam polishing method was used in this study to improve surface quality. In this process, an electron beam with a maximum diameter of 60 mm was applied for a few microseconds to melt and evaporate a metal surface. Al6061 and SUS304 metal plates were prepared with different geometric patterns and subjected to electron beam polishing. The surface roughness of the patterned SUS304 metal plate was significantly improved. However, the surface roughness of the patterned Al6061 metal plate became worse. Although the surface hardness decreased by approximately 10% on the re-solidified layers on both types of plates, the contact angle increased due to changes in surface morphology. The microstructure variation after the electron beam irradiation was also examined and compared with the thickness prediction of the re-solidified layer for Al6061 and SUS304 metal plates.

  9. Electron beam deposition for nanofabrication : Insights from surface science

    NARCIS (Netherlands)

    Wnuk, J. D.; Rosenberg, S. G.; Gorham, J. M.; van Dorp, W. F.; Hagen, C. W.; Fairbrother, D. H.

    2011-01-01

    Electron beam induced deposition (EBID) is a direct-write lithographic technique that utilizes the dissociation of volatile precursors by a focused electron beam in a low vacuum environment to create nanostructures. Notable advantages of EBID over competing lithographic techniques are that it is a s

  10. Electronic Structure of Single-Crystal Monolayer Graphene on Hydrogen-Terminated Germanium Surface

    Science.gov (United States)

    Ahn, Sung Joon; Lee, Jae-Hyun; Ahn, Joung Real; Whang, Dongmok

    2015-03-01

    Graphene, atomically flat 2-Dimensional layered nano material, has a lot of interesting characteristics from its unusual electronic structure. Almost properties of graphene are influenced by its crystallinity, therefore the uniform growth of single crystal graphene and layer control over the wafer scale areas remains a challenge in the fields of electronic, photonic and other devices based on graphene. Here, we report the method to make wafer scale single crystal monolayer graphene on hydrogen terminated germanium(110) surface and properties and electronic band structure of the graphene by using the tool of scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, electron transport measurement, electron diffraction and angle-resolved photoemission spectroscopy.

  11. Electron beam processed plasticized epoxy coatings for surface protection

    Energy Technology Data Exchange (ETDEWEB)

    Ibrahim, Mervat S. [National Center for Radiation Research and Technology, Nasr City (Egypt); Mohamed, Heba A., E-mail: hebaamohamed@gmail.com [National Research Center, Dokki (Egypt); Kandile, Nadia G. [University College for Girls, Ain Shams University (Egypt); Said, Hossam M.; Mohamed, Issa M. [National Center for Radiation Research and Technology, Nasr City (Egypt)

    2011-10-17

    Highlights: {center_dot} Coating formulations with EA 70%, HD 20%, and castor oil 10% under 1 Mrad pass{sup -1} irradiation dose showed the best adhesion and passed bending tests. {center_dot} The prepared EP-SF-An adduct improve anti-corrosion properties of coatings without any significant effect on physical, mechanical and chemical properties of the cured film. The optimum amount of aniline adduct as corrosion inhibitor was found to be 0.4 g for 100 g of coating formulation. {center_dot} The corrosion inhibition efficiency of the prepared adduct competed the commercial efficiency. - Abstract: Epoxy acrylate oligomer (EA) was plasticized by adding different plasticizers such as epoxidized soybean oil, glycerol and castor oil and cured by electron beam (EB). Different irradiation doses (1, 2.5 and 5 Mrad pass{sup -1}) were used in the curing process. The effect of both different irradiation doses and plasticizers on the end use performance properties of epoxy acrylate coating namely, pencil hardness, bending test, adhesion test, acid and alkali resistance test were studied. It was observed that incorporation of castor oil in epoxy acrylate diluted by 1,6-hexanediol diacrylate (HD) monomer with a ratio (EA 70%, HD 20%, castor oil 10%) under 1 Mrad pass{sup -1} irradiation dose improved the physical, chemical and mechanical properties of cured films than the other plasticizer. Sunflower free fatty acid was epoxidized in situ under well established conditions. The epoxidized sunflower free fatty acids (ESFA) were subjected to react with aniline in sealed ampoules under inert atmosphere at 140 deg. C. The produced adducts were added at different concentrations to epoxy acrylate coatings under certain EB irradiation dose and then evaluated as corrosion inhibitors for carbon steel surfaces in terms of weight loss measurements and corrosion resistance tests. It was found that, addition of 0.4 g of aniline adduct to 100 g epoxy acrylate formula may give the best corrosion

  12. Aspects of Metal Surface Glowing Mechanisms with Intensive Electron Beam Bombardment

    Directory of Open Access Journals (Sweden)

    I.V. Barsuk

    2012-06-01

    Full Text Available The paper gives a brief description and analysis of the main physical processes which can have an effect on the glowing nature of metal element surfaces in different electric vacuum devices when they are bombarded by electron beams. It has been found that the electron glowing effects on metal surfaces according to the electron energy can be explained with the help of the transition scattering on plasma waves or just with the classical transition radiation effect. This fact is rather important in terms of classical physics interpretation of the observed glowing effects on metal surface elements and techniques optimization of metal and electron beams diagnostics as well.

  13. Modeling of Reduced Effective Secondary Electron Emission Yield from a Velvet Surface

    CERN Document Server

    Swanson, Charles

    2016-01-01

    Complex structures on a material surface can significantly reduce total secondary electron emission from that surface. A velvet is a surface that consists of an array of vertically standing whiskers. The reduction occurs due to the capture of low-energy, true secondary electrons emitted at the bottom of the structure and on the sides of the velvet whiskers. We performed numerical simulations and developed an approximate analytical model that calculates the net secondary electron emission yield from a velvet surface as a function of the velvet whisker length and packing density, and the angle of incidence of primary electrons. The values of optimal velvet whisker packing density that maximally suppresses secondary electron emission yield are determined as a function of velvet aspect ratio and electron angle of incidence.

  14. The Role of Substrate Electrons in the Wetting of a Metal Surface

    Energy Technology Data Exchange (ETDEWEB)

    Schiros, T.; Takahashi, O.; Andersson, K.J.; Ostrom, H.; Pettersson, L.G.M.; Nilsson, A.; Ogasawara, H.; /SLAC

    2012-04-18

    We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution of charge that enables surface wetting. On open d-shell Pt(111), the ligand field of water alters the distribution of metal d-electrons to reduce the repulsion. The closed-shell Cu d{sup 10} configuration of isostructural Cu(111), however, does not afford this mechanism, resulting in a hydrophobic surface and three-dimensional ice cluster formation. On the geometrically corrugated Cu(110) surface, however, charge depletion involving the mobile sp-electrons at atomic rows reduces the exchange repulsion sufficiently such that formation of a two-dimensional wetting layer is still favored in spite of the d{sup 10} electronic configuration.

  15. Nonadiabaticity and single-electron transport driven by surface acoustic waves

    DEFF Research Database (Denmark)

    Flensberg, Karsten; Niu, Q.; Pustilnik, M.

    1999-01-01

    Single-electron transport driven by surface acoustic waves (SAW) through a narrow constriction, formed in a two-dimensional electron gas, is studied theoretically. Due to long-range Coulomb interaction, the tunneling coupling between the electron gas and the moving minimum of the SAW...

  16. The role of substrate electrons in the wetting of a metal surface

    DEFF Research Database (Denmark)

    Schiros, T.; Takahashi, O.; Andersson, Klas Jerker;

    2010-01-01

    We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution of...

  17. The effect of hot electrons and surface plasmons on heterogeneous catalysis

    Science.gov (United States)

    Kim, Sun Mi; Lee, Si Woo; Moon, Song Yi; Park, Jeong Young

    2016-06-01

    Hot electrons and surface-plasmon-driven chemistry are amongst the most actively studied research subjects because they are deeply associated with energy dissipation and the conversion processes at the surface and interfaces, which are still open questions and key issues in the surface science community. In this topical review, we give an overview of the concept of hot electrons or surface-plasmon-mediated hot electrons generated under various structural schemes (i.e. metals, metal-semiconductor, and metal-insulator-metal) and their role affecting catalytic activity in chemical reactions. We highlight recent studies on the relation between hot electrons and catalytic activity on metallic surfaces. We discuss possible mechanisms for how hot electrons participate in chemical reactions. We also introduce controlled chemistry to describe specific pathways for selectivity control in catalysis on metal nanoparticles.

  18. 78 FR 36768 - Electron Hydro, LLC; Supplemental Notice That Initial Market-Based Rate Filing Includes Request...

    Science.gov (United States)

    2013-06-19

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF ENERGY Federal Energy Regulatory Commission Electron Hydro, LLC; Supplemental Notice That Initial Market- Based Rate...-referenced proceeding, of Electron Hydro, LLC's application for market-based rate authority, with...

  19. Electronic Structure of Solids and Their Surfaces and Interfaces.

    Science.gov (United States)

    1981-06-30

    point and several articles relating to these studies are being prepared for publication. I. ~ -- ~ i n’J This irnvest.gf.gation has the iur-Pose of...the ideal terminated cubic ,- cristobalite ) surface. Using an admittedly crude model for the surface, they found no states in the band gap. The purpose...this level is an E’ center at or near the surface ( ). The method of sample preparation which they have used (grinding) could easily have caused

  20. Collaborative Research: Fundamental studies of plasma control using surface embedded electronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Raja, Laxminarayan L. [Univ. of Texas, Austin, TX (United States); PanneerChelvam, PremKumar [Univ. of Texas, Austin, TX (United States); Levko, Dimtry [Univ. of Texas, Austin, TX (United States)

    2016-02-26

    The proposed study will investigate the effect of active electron injection of from electrode surfaces To the best of our knowledge, no such a study has ever been attempted even though it could lead to the formation of whole new classes of plasma based devices and systems. We are motivated by recent articles and simple theory which gives strong reason to believe that embedded electronic devices can be used to exert control over the SEE coefficient of semiconductor surfaces (and maybe other surface types as well). Furthermore, the research will explore how such sub-surface electronic devices can best be used to exert control over an associated plasma.

  1. Electron beam induced oxidation of Ni3Al surfaces : electron flux effects

    NARCIS (Netherlands)

    Koch, S.A.; Palasantzas, G.; Agterveld, D.T.L. van; Hosson, J.Th.M. De

    2002-01-01

    Electron beam irradiation of polycrystalline boron doped Ni3Al (at 300 K and under ultrahigh vacuum conditions) induces fast oxidation. The rate and depth of oxidation initially increase with increasing electron flux as indicated by results from Auger electron spectroscopy. Curves of oxygen developm

  2. Electron Conditioning of Technical Aluminium Surfaces: Effect on the Secondary Electron Yield

    Energy Technology Data Exchange (ETDEWEB)

    Le Pimpec, F.

    2004-12-13

    The effect of electron conditioning on commercially aluminium alloys 1100 and 6063 were investigated. Contrary to the assumption that electron conditioning, if performed long enough, can reduce and stabilize the SEY to low values (< 1.3, value of many pure elements [1] ), the SEY of aluminium did not go lower than 1.8. In fact, it reincreases with continued electron exposure dose.

  3. Self-consistent electronic structure and segregation profiles of the Cu-Ni (001) random-alloy surface

    DEFF Research Database (Denmark)

    Ruban, Andrei; Abrikosov, I. A.; Kats, D. Ya.

    1994-01-01

    We have calculated the electronic structure and segregation profiles of the (001) surface of random Cu-Ni alloys with varying bulk concentrations by means of the coherent potential approximation and the linear muffin-tin-orbitals method. Exchange and correlation were included within the local-den...... to be oscillatory with a strong preference for Cu to segregate towards the surface of the alloy....

  4. Low-energy electron irradiation induced top-surface nanocrystallization of amorphous carbon film

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Cheng [Institute of Nanosurface Science and Engineering (INSE), Shenzhen University, Shenzhen 518060 (China); Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060 (China); Fan, Xue, E-mail: fanx@szu.edu.cn [Institute of Nanosurface Science and Engineering (INSE), Shenzhen University, Shenzhen 518060 (China); Diao, Dongfeng, E-mail: dfdiao@szu.edu.cn [Institute of Nanosurface Science and Engineering (INSE), Shenzhen University, Shenzhen 518060 (China)

    2016-10-30

    Graphical abstract: Low-energy electron irradiation was proposed to nanocrystallize the top-surface of the as-deposited amorphous carbon film, and sp{sup 2} nanocrystallites formed in the film top-surface within 4 nm thickness. Display Omitted - Abstract: We report a low-energy electron irradiation method to nanocrystallize the top-surface of amorphous carbon film in electron cyclotron resonance plasma system. The nanostructure evolution of the carbon film as a function of electron irradiation density and time was examined by transmission electron microscope (TEM) and Raman spectroscopy. The results showed that the electron irradiation gave rise to the formation of sp{sup 2} nanocrystallites in the film top-surface within 4 nm thickness. The formation of sp{sup 2} nanocrystallite was ascribed to the inelastic electron scattering in the top-surface of carbon film. The frictional property of low-energy electron irradiated film was measured by a pin-on-disk tribometer. The sp{sup 2} nanocrystallized top-surface induced a lower friction coefficient than that of the original pure amorphous film. This method enables a convenient nanocrystallization of amorphous surface.

  5. Comparison of contact angle measurement and microbial adhesion to solvents for assaying electron donor-electron acceptor (acid-base) properties of bacterial surface.

    Science.gov (United States)

    Hamadi, Fatima; Latrache, Hassan

    2008-08-01

    The electron donor-electron acceptor (acid-base properties) of cell surfaces of a series of bacteria were determined by two methods, namely, Microbial Adhesion to Solvents (MATS) and Contact Angle Measurements (CAM) combined with equation of Van Oss. The efficiency of these two methods was then compared. Pseudomonas aeruginosa ATCC 27853, Bacillus subtilis ILP 142B, Staphylococcus aureus ATCC 25923 and four Escherichia coli strains including HB101, AL52, O128B12 and ATCC 25922, acid-base properties were examined under the two different conditions mentioned above. The results showed that the correlation between acid-base properties determined by MATS and CAM was very weak. We have also found that when the microbial cell surface was electron donor by CAM method, similar result was found by MATS, but the reverse was not always true. In contrast, a good correlation between the two methods was obtained when the four E. coli strains were examined.

  6. Surface structure of Bi2Se3(111) determined by low-energy electron diffraction and surface x-ray diffraction

    DEFF Research Database (Denmark)

    dos Reis, Diogo Duarte; Barreto, Lucas; Bianchi, Marco

    2013-01-01

    The surface structure of the prototypical topological insulator Bi2Se3 is determined by low-energy electron diffraction and surface x-ray diffraction at room temperature. Both approaches show that the crystal is terminated by an intact quintuple layer. Specifically, an alternative termination by ...... by a bismuth bilayer is ruled out. Surface relaxations obtained by both techniques are in good agreement with each other and found to be small. This includes the relaxation of the van der Waals gap between the first two quintuple layers....

  7. Imaging of surface spin textures on bulk crystals by scanning electron microscopy.

    Science.gov (United States)

    Akamine, Hiroshi; Okumura, So; Farjami, Sahar; Murakami, Yasukazu; Nishida, Minoru

    2016-11-22

    Direct observation of magnetic microstructures is vital for advancing spintronics and other technologies. Here we report a method for imaging surface domain structures on bulk samples by scanning electron microscopy (SEM). Complex magnetic domains, referred to as the maze state in CoPt/FePt alloys, were observed at a spatial resolution of less than 100 nm by using an in-lens annular detector. The method allows for imaging almost all the domain walls in the mazy structure, whereas the visualisation of the domain walls with the classical SEM method was limited. Our method provides a simple way to analyse surface domain structures in the bulk state that can be used in combination with SEM functions such as orientation or composition analysis. Thus, the method extends applications of SEM-based magnetic imaging, and is promising for resolving various problems at the forefront of fields including physics, magnetics, materials science, engineering, and chemistry.

  8. Unravelling surface and interfacial structures of a metal–organic framework by transmission electron microscopy

    KAUST Repository

    Zhu, Yihan

    2017-02-21

    Metal–organic frameworks (MOFs) are crystalline porous materials with designable topology, porosity and functionality, having promising applications in gas storage and separation, ion conduction and catalysis1, 2, 3. It is challenging to observe MOFs with transmission electron microscopy (TEM) due to the extreme instability of MOFs upon electron beam irradiation4, 5, 6, 7. Here, we use a direct-detection electron-counting camera to acquire TEM images of the MOF ZIF-8 with an ultralow dose of 4.1 electrons per square ångström to retain the structural integrity. The obtained image involves structural information transferred up to 2.1 Å, allowing the resolution of individual atomic columns of Zn and organic linkers in the framework. Furthermore, TEM reveals important local structural features of ZIF-8 crystals that cannot be identified by diffraction techniques, including armchair-type surface terminations and coherent interfaces between assembled crystals. These observations allow us to understand how ZIF-8 crystals self-assemble and the subsequent influence of interfacial cavities on mass transport of guest molecules.

  9. Unravelling surface and interfacial structures of a metal-organic framework by transmission electron microscopy

    Science.gov (United States)

    Zhu, Yihan; Ciston, Jim; Zheng, Bin; Miao, Xiaohe; Czarnik, Cory; Pan, Yichang; Sougrat, Rachid; Lai, Zhiping; Hsiung, Chia-En; Yao, Kexin; Pinnau, Ingo; Pan, Ming; Han, Yu

    2017-05-01

    Metal-organic frameworks (MOFs) are crystalline porous materials with designable topology, porosity and functionality, having promising applications in gas storage and separation, ion conduction and catalysis. It is challenging to observe MOFs with transmission electron microscopy (TEM) due to the extreme instability of MOFs upon electron beam irradiation. Here, we use a direct-detection electron-counting camera to acquire TEM images of the MOF ZIF-8 with an ultralow dose of 4.1 electrons per square ångström to retain the structural integrity. The obtained image involves structural information transferred up to 2.1 Å, allowing the resolution of individual atomic columns of Zn and organic linkers in the framework. Furthermore, TEM reveals important local structural features of ZIF-8 crystals that cannot be identified by diffraction techniques, including armchair-type surface terminations and coherent interfaces between assembled crystals. These observations allow us to understand how ZIF-8 crystals self-assemble and the subsequent influence of interfacial cavities on mass transport of guest molecules.

  10. An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

    Science.gov (United States)

    Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus

    2015-12-01

    We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

  11. An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

    Energy Technology Data Exchange (ETDEWEB)

    Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus, E-mail: cropers@gwdg.de [4th Physical Institute - Solids and Nanostructures, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany)

    2015-12-07

    We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

  12. A split-step method to include electron–electron collisions via Monte Carlo in multiple rate equation simulations

    Energy Technology Data Exchange (ETDEWEB)

    Huthmacher, Klaus [Department of Physics and OPTIMAS Research Center, University of Kaiserslautern (Germany); Molberg, Andreas K. [Department of Chemistry and OPTIMAS Research Center, University of Kaiserslautern (Germany); Rethfeld, Bärbel [Department of Physics and OPTIMAS Research Center, University of Kaiserslautern (Germany); Gulley, Jeremy R., E-mail: jgulley@kennesaw.edu [Department of Physics, Kennesaw State University, Kennesaw, GA 30144 (United States)

    2016-10-01

    A split-step numerical method for calculating ultrafast free-electron dynamics in dielectrics is introduced. The two split steps, independently programmed in C++11 and FORTRAN 2003, are interfaced via the presented open source wrapper. The first step solves a deterministic extended multi-rate equation for the ionization, electron–phonon collisions, and single photon absorption by free-carriers. The second step is stochastic and models electron–electron collisions using Monte-Carlo techniques. This combination of deterministic and stochastic approaches is a unique and efficient method of calculating the nonlinear dynamics of 3D materials exposed to high intensity ultrashort pulses. Results from simulations solving the proposed model demonstrate how electron–electron scattering relaxes the non-equilibrium electron distribution on the femtosecond time scale.

  13. Electronic structures of the oxygenated diamond (100)surfaces

    Institute of Scientific and Technical Information of China (English)

    LIU Fengbin; WANG Jiadao; LIU Bing; LI Xuemin; CHEN Darong

    2006-01-01

    By means of first principles method on the basis of density functional theory (DFT), the equilibrium geometries and density of states (DOS) of the two oxygenated diamond (100) surfaces, bridging model and on-top model are calculated. The results indicate that there are no surface states located in the band gap of the bridging model of oxygenated diamond (100) surface, and the occupied surface states in the valence band are attributed to the non-bonded O 2p orbital, O 2p and C 2p bonding orbitals, and C 2p and H1s bonding orbitals. By contrast, for the on-top model of oxygenated diamond (100) surface,the unoccupied surface states exist in the band gap,which originate from non-bonded C 2p and O 2p orbitals. In addition, the occupied surface states in the valence band are induced by non-bonded O 2p orbital and the C=O π bond.

  14. Electronic and structural properties of the (1010) and (1120) ZnO surfaces.

    Science.gov (United States)

    Marana, N L; Longo, V M; Longo, E; Martins, J B L; Sambrano, J R

    2008-09-25

    The structural and electronic properties of ZnO (1010) and (1120) surfaces were investigated by means of density functional theory applied to periodic calculations at B3LYP level. The stability and relaxation effects for both surfaces were analyzed. The electronic and energy band properties were discussed on the basis of band structure as well as density of states. There is a significant relaxation in the (1010) as compared to the (1120) terminated surfaces. The calculated direct gap is 3.09, 2.85, and 3.09 eV for bulk, (1010), and (1120) surfaces, respectively. The band structures for both surfaces are very similar.

  15. Quantitative Agreement between Electron-Optical Phase Images of WSe2 and Simulations Based on Electrostatic Potentials that Include Bonding Effects

    Science.gov (United States)

    Borghardt, S.; Winkler, F.; Zanolli, Z.; Verstraete, M. J.; Barthel, J.; Tavabi, A. H.; Dunin-Borkowski, R. E.; Kardynal, B. E.

    2017-02-01

    The quantitative analysis of electron-optical phase images recorded using off-axis electron holography often relies on the use of computer simulations of electron propagation through a sample. However, simulations that make use of the independent atom approximation are known to overestimate experimental phase shifts by approximately 10%, as they neglect bonding effects. Here, we compare experimental and simulated phase images for few-layer WSe2 . We show that a combination of pseudopotentials and all-electron density functional theory calculations can be used to obtain accurate mean electron phases, as well as improved atomic-resolution spatial distribution of the electron phase. The comparison demonstrates a perfect contrast match between experimental and simulated atomic-resolution phase images for a sample of precisely known thickness. The low computational cost of this approach makes it suitable for the analysis of large electronic systems, including defects, substitutional atoms, and material interfaces.

  16. Ab initio effective core potentials including relativistic effects and their application to the electronic structure calculations of heavy atoms and molecules

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y.S.

    1977-11-01

    The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed in detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials.

  17. Low energy high current pulsed electron beam treatment for improving surface microstructure and properties

    Energy Technology Data Exchange (ETDEWEB)

    Wu, J; Allain-Bonasso, N; Zhang, X D; Hao, S Z; Grosdider, T; Dong, C [Laboratoire d' Etude des Textures et Applications aux Materiaux (LETAM, UMR-CNRS 3143), Universite Paul Verlaine-Metz, Ile du Saulcy, 57045 Metz (France); Zou, J X, E-mail: jiang.wu@univ-metz.fr, E-mail: thierry.grosdidier@univ-metz.fr [National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2010-06-15

    Low energy high current pulsed electron beam (LEHCPEB) is a fairly new technique for surface modifications authorizing improvement in wear and corrosion properties as well as texture changes and hardening. This contribution highlights some microstructure modifications encountered at the surface of HCPEB treated steels and bulk metallic glasses taking into account the effects of surface melting and the effects of the induced stress.

  18. Primary role of electron work function for evaluation of nanostructured titania implant surface against bacterial infection.

    Science.gov (United States)

    Golda-Cepa, M; Syrek, K; Brzychczy-Wloch, M; Sulka, G D; Kotarba, A

    2016-09-01

    The electron work function as an essential descriptor for the evaluation of metal implant surfaces against bacterial infection is identified for the first time. Its validity is demonstrated on Staphylococcus aureus adhesion to nanostructured titania surfaces. The established correlation: work function-bacteria adhesion is of general importance since it can be used for direct evaluation of any electrically conductive implant surfaces.

  19. Electron mean free path dependence of the vortex surface impedance

    Science.gov (United States)

    Checchin, M.; Martinello, M.; Grassellino, A.; Romanenko, A.; Zasadzinski, J. F.

    2017-03-01

    In the present study the radio-frequency complex response of trapped vortices in superconductors is calculated and compared to experimental data previously published. The motion equation for a magnetic flux line is solved assuming a bi-dimensional and mean-free-path-dependent Lorentzian-shaped pinning potential. The resulting surface resistance shows the unprecedented bell-shaped trend as a function of the mean-free-path observed in our previous experimental work. We demonstrate that such bell-shaped trend of the surface resistance as a function of the mean-free-path may be described as the interplay of the two limiting regimes of the surface resistance, for low and large mean-free-path values: pinning and flux-flow regimes respectively. Since the possibility of defining the pinning potential at different locations from the surface and with different strengths, we discuss how the surface resistance is affected by different configurations of pinning sites. By tackling the frequency dependence of the surface resistance, we also demonstrate that the separation between pinning- and flux-flow-dominated regimes cannot be determined only by the depinning frequency. The dissipation regime can be tuned either by acting on the frequency or on the mean-free-path value.

  20. Photoelectron spectroscopy and Auger electron spectroscopy of solids and surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kowalczyk, S.P.

    1976-01-01

    The use of photoelectron spectroscopy, primarily x-ray photoelectron spectroscopy, to obtain information on the electronic structure of a wide variety of solids (especially the bulk electronic structure of solids) is covered. Both valence band and core-level spectra, as well as a few cases of photon excited Auger electron spectroscopy, are employed in the investigations to derive information on N(E). The effect of several modulations inherent in the measured I(E)'s, such as final state band structure, cross section, and relaxation, is discussed. Examples of many-electron interactions in PES are given. Some experimental aspects of PES and AES studies are given with emphasis on sample preparation techniques. Multiple splitting of core levels is examined using the Mn levels in MnF/sub 2/ as a detailed case study. Core level splittings in transition metals, rare earth metals, transition metal halides and several alloys are also reported. The application of PES to the study of the chemical bond in some crystalline semiconductors and insulators, A/sup N/B/sup 8-N/ and A/sup N/B/sup 10-N/ compounds is treated, and a spectroscopic scale of ionicity for these compounds is developed from the measured ''s-band'' splitting in the valence band density of states. (GHT)

  1. Negative plasma potential relative to electron-emitting surfaces.

    Science.gov (United States)

    Campanell, M D

    2013-09-01

    Most works on plasma-wall interaction predict that with strong electron emission, a nonmonotonic "space-charge-limited" (SCL) sheath forms where the plasma potential is positive relative to the wall. We show that a fundamentally different sheath structure is possible where the potential monotonically increases toward a positively charged wall that is shielded by a single layer of negative charge. No ion-accelerating presheath exists in the plasma and the ion wall flux is zero. An analytical solution of the "inverse sheath" regime is demonstrated for a general plasma-wall system where the plasma electrons and emitted electrons are Maxwellian with different temperatures. Implications of the inverse sheath effect are that (a) the plasma potential is negative, (b) ion sputtering vanishes, (c) no charge is lost at the wall, and (d) the electron energy flux is thermal. To test empirically what type of sheath structure forms under strong emission, a full plasma bounded by strongly emitting walls is simulated. It is found that inverse sheaths form at the walls and ions are confined in the plasma. This result differs from past particle-in-cell simulation studies of emission which contain an artificial "source sheath" that accelerates ions to the wall, leading to a SCL sheath at high emission intensity.

  2. Surface plasmon enhanced interfacial electron transfer and resonance Raman, surface-enhanced resonance Raman studies of cytochrome C mutants

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Junwei

    1999-11-08

    Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO{sub 2} were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO{sub 2}, large photoelectrocatalytic effect for the reduction of CO{sub 2} was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO{sub 2} in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.

  3. Surface plasmon enhanced interfacial electron transfer and resonance Raman, surface-enhanced resonance Raman studies of cytochrome C mutants

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Junwei [Iowa State Univ., Ames, IA (United States)

    1999-11-08

    Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO2 were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO2, large photoelectrocatalytic effect for the reduction of CO2 was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO2 in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.

  4. Glass for parenteral products: a surface view using the scanning electron microscope.

    Science.gov (United States)

    Roseman, T J; Brown, J A; Scothorn, W W

    1976-01-01

    The scanning electron microscope was utilized to explore the internal surface of glass ampuls and vials used in parenteral products. The surface topography of USP Type I borosilicate glass containers was viewed after exposure to "sulfur," ammonium bifluoride, and sulfuric acid treatments. The scanning electron micrographs showed startling differences in the appearance of the surface regions. "Sulfur treatment" of ampuls was associated with a pitting of the surface and the presence of sodium sulfate crystals. The sulfur treatment of vials altered the glass surface in a characteristically different manner. The dissimilarity between the surface appearances was attributed to the method of sulfur treatment. Ampuls exposed to sulfuric acid solutions at room temperature did not show the pitting associated with the sulfur treatment. Scanning electron micrographs of ammonium bifluoride-treated ampuls showed a relief effect, suggesting that the glass was affected by the bifluoride solution but that sufficient stripping of the surface layer did not occur to remove the pits associated with the sulfur treatment. Flakes emanating from the glass were identified with the aid of the electron microprobe. Scanning electron micrographs showed that these vitreous flakes resulted from a delamination of a thin layer of the glass surface. It is concluded that the scanning electron microscope, in conjunction with other analytical techniques, is a valuable tool in assessing the quality of glass used for parenteral products. The techniques studied should be of particular importance to the pharmaceutical industry where efforts are being made to reduce the levels of particulate matter in parenteral dosage forms.

  5. Secondary Electron Yield on Cryogenic Surfaces as a Function of Physisorbed Gases

    CERN Document Server

    Kuzucan, Asena; Taborelli, Mauro

    2011-01-01

    In LHC the electron cloud induced by photoelectrons, gas ionization and secondary electrons emitted from the beam pipe walls could be a limitation of the performance. The electron cloud induce heat load on the cryogenic system, cause pressure rise, emittance growth and beam instabilities, which in the end will limit the beam’s lifetime. Beam- induced multipacting, which can arise through oscillatory motion of photoelectrons and low-energy secondary electrons bouncing back and forth between opposite walls of the vacuum chamber during successive passage of proton bunches, represent therefore a potential problem for the machine. The secondary electron yield (SEY) is one of the key parameters for the electron cloud build up and multipacting phenomenon. An electron cloud occurs if the metal surface secondary electron yield is high enough for electron multiplication. This parameter has been extensively studied on room temperature samples but uncertainties remain for samples at cryogenic temperature. Indeed, at l...

  6. Excitation and charge transfer in He/sup +/ + H collisions. A molecular approach including two-electron translation factors

    Energy Technology Data Exchange (ETDEWEB)

    Errea, L.F.; Mendez, L.; Riera, A.

    1983-06-01

    In a previous paper we have pointed out that the common-translation-factor (CTF) method is the only one which, at present, and within the framework of the molecular model of atomic collisions, can be shown to be both convergent and computationally fast, even for many-electron systems. In this Communication we check that this second statement is correct, presenting, for the first time, a molecular calculation involving two-electron translation factors, for He/sup +/ + H collisions. A careful study of the sensitivity of the calculated cross sections to the choice of the CTF is performed, and conclusions on that sensitivity are drawn, for several types of processes.

  7. Electron emission induced by resonant coherent ion-surface interaction at grazing incidence

    Energy Technology Data Exchange (ETDEWEB)

    Garcia de Abajo, F.J. (Departamento de Ciencias de la Computacion e Inteligencia Artificial, Facultad de Informatica, Universidad del Pais Vasco, Apartado 649, 20080 San Sebastian (Spain)); Ponce, V.H. (Centro Atomico Bariloche, Comision Nacional de Energia Atomica, 8400 San Carlos de Bariloche, Rio Negro (Argentina)); Echenique, P.M. (Departamento de Fisica de Materiales, Facultad de Quimica, Universidad del Pais Vasco, Apartado 1072, 20080 San Sebastian (Spain))

    1992-10-19

    A new spectroscopy based on the resonant coherently induced electron loss to the continuum in ion-surface scattering under grazing incidence is proposed. A series of peaks, corresponding to the energy differences determined by the resonant interaction with the rows of atoms in the surface, is predicted to appear in the energy distribution of electrons emitted from electronic states bound to the probe. Calculations for MeV He{sup +} ions scattered at a W(001) surface along the {l angle}100{r angle} direction with a glancing angle of 0--2 mrad show a total yield close to 1.

  8. Field-Emission from Chemically Functionalized Diamond Surfaces: Does Electron Affinity Picture Work?

    Science.gov (United States)

    Miyamoto, Yoshiyuki; Miyazaki, Takehide; Takeuchi, Daisuke; Okushi, Hideyo; Yamasaki, Satoshi

    2014-03-01

    By means of the time-dependent density functional electron dynamics, we have revisited the field-emission efficiency of chemically functionalized diamond (100) surfaces. In order to achieve high efficiency and high (chemical) stability, proper chemical species are needed to terminate diamond surfaces. Hydrogen (H) termination is well known to achieve the negative electron affinity (NEA) of diamond surface which indeed enhances field emission performance than that of clean surface with positive electron affinity (PEA). Yet, the durability of H-terminated diamond surface was concerned for long-time operation of the field-emission. Meantime, oxidation, or hydroxyl (OH) termination was considered to achieve chemical stability of the surface but presence of oxygen (O) atom should reduce the emission efficiency. Recently, H- OH-co-terminated surface is reported as NEA and was expected to achieve both emission efficiency and chemical stability. However, our simulation showed that emission efficiency of the H- OH- co-terminated surface is much lower than clean surface with PEA, thus we note that the electron affinity cannot be a unique measure to determine the emission efficiency. In this talk, we introduce necessity of new concept to understand the emission efficiency which needs to know detailed potential profile from bulk to vacuum through surface, which is strongly dependent on the surface chemical functionalization. This work was supported by ALCA project conducted by Japan Science and Technology Agency.

  9. Electronic dissipation processes during chemical reactions on surfaces

    CERN Document Server

    Stella, Kevin

    2012-01-01

    Hauptbeschreibung Every day in our life is larded with a huge number of chemical reactions on surfaces. Some reactions occur immediately, for others an activation energy has to be supplied. Thus it happens that though a reaction should thermodynamically run off, it is kinetically hindered. Meaning the partners react only to the thermodynamically more stable product state within a mentionable time if the activation energy of the reaction is supplied. With the help of catalysts the activation energy of a reaction can be lowered. Such catalytic processes on surfaces are widely used in industry. A

  10. Local electronic properties of graphene flakes on noble metal surfaces

    OpenAIRE

    Leicht, Philipp

    2015-01-01

    This thesis examines possible routes for the preparation of graphene nanostructures on metal substrates and performs structural and electronic characterizations using scanning tunneling microcopy and spectroscopy. Investigations of graphene nanostructures necessitate the use of a suitable graphene-substrate combination, which allows for a controlled in situ preparation of small and well-shaped graphene nanostructures. The choice of a graphene-substrate combination with weak interaction in or...

  11. Electronic structure of reconstructed InAs(001) surfaces - identification of bulk and surface bands based on their symmetries

    Science.gov (United States)

    Olszowska, Natalia; Kolodziej, Jacek J.

    2016-02-01

    Using angle-resolved photoelectron spectroscopy (ARPES) band structures of indium- and arsenic-terminated InAs(001) surfaces are investigated. These surfaces are highly reconstructed, elementary cells of their lattices contain many atoms in different chemical configurations, and moreover, they are composed of domains having related but different reconstructions. These domain-type surface reconstructions result in the reciprocal spaces containing regions with well-defined k→∥-vector and regions with not-well-defined one. In the ARPES spectra most of the surface related features appear as straight lines in the indeterminate k→∥-vector space. It is shown that, thanks to differences in crystal and surface symmetries, the single photon energy ARPES may be successfully used for classification of surface and bulk bands of electronic states on complex, highly reconstructed surfaces instead of the most often used variable photon energy studies.

  12. Magnetite Fe3O4 (111) Surfaces: Impact of Defects on Structure, Stability, and Electronic Properties

    KAUST Repository

    Noh, Junghyun

    2015-08-04

    We present a comprehensive investigation, via first-principles density functional theory (DFT) calculations, of various surface terminations of magnetite, Fe3O4 (111), a major iron oxide which has also a number of applications in electronics and spintronics. We compare the thermodynamic stability and electronic structure among the different surfaces terminations. Interestingly, we find that surfaces modified with point defects and adatoms can be more stable than bulk-like terminations. These surfaces show different surface chemistry, electronic structures and distinctive spin polarization features near the Fermi level from those previously considered in the literature. Our studies provide an atomic level insight for magnetite surfaces, which is a necessary step to understanding their interfaces with organic layers in OLED and spintronic devices.

  13. Atomic and Electronic Structures of Cd0.96Zn0.04Te(110) Surface

    Institute of Scientific and Technical Information of China (English)

    ZHA Gang-Qiang; JIE Wan-Qi; ZHANG Wen-Hua; LI Qiang; XU Fa-Qiang

    2005-01-01

    @@ X-Ray diffraction is used to analyse the lattice structure of Cd0.96Zn0.04Te (CZT), and the lattice constant is measured to be 0.647nm. The atomic structure of the clean CZT(110) surface obtained by Ar+ etching in vacuum is observed by low-energy electron diffraction, where no surface reconstruction is discovered. Angleresolved photoemission spectroscopy was used to characterize the surface state of the clean CZT (110) surface,by which we find a 1.5-eV-wide surface band with the peak at 0.9eV below the Fermi energy containing about6.9 × 1014 electrons/cm2, approximately one electron per surface atom.

  14. 75 FR 38127 - Visteon Systems, LLC North Penn Plant Electronics Products Group Including On-Site Leased Workers...

    Science.gov (United States)

    2010-07-01

    ... Employment and Training Administration Visteon Systems, LLC North Penn Plant Electronics Products Group... Adjustment Assistance and Alternative Trade Adjustment Assistance In accordance with Section 223 of the Trade Act of 1974 (19 U.S.C. 2273), and Section 246 of the Trade Act of 1974 (26 U.S.C. 2813), as...

  15. The electronic structure of NiO for Ni 3s-hole states including full orbital relaxation and localization

    NARCIS (Netherlands)

    Bagus, Paul S.; Broer, R; Graaf, C. de; Nieuwpoort, W.C.

    1999-01-01

    The electronic structure of NiO, with emphasis on the Ni 3s-hole ionic states, is studied using non-orthogonal configuration interaction, NOCI, wavefunctions for an NiO6 model of the crystal. Orbital sets are relaxed, or optimized, separately for each configuration used in the NOCI and orbital

  16. Electronic structure of the surface unoccupied band of Ge(001)-c (4 ×2 ) : Direct imaging of surface electron relaxation pathways

    Science.gov (United States)

    Kanasaki, J.; Yamamoto, I.; Azuma, J.; Fukatsu, S.

    2017-09-01

    We have studied the electronic structure of the surface unoccupied band (SUB) of clean Ge(001)-c (4 ×2 ) , with high energy and momentum resolution, by means of time- and angle-resolved two-photon photoelectron spectroscopy. The time evolution of photoelectron intensity images, measured as functions of energy and emission angle after photoexcitation with laser pulses (1.5 eV, 200 fs), provides a momentum space view of the relaxation pathways of surface excited electrons toward the bottom of the SUB. Surface excited electrons relax in several picoseconds along the strongly dispersive directions (Γ ¯J'¯ and Γ ¯J2 '¯ ) and then accumulate near the band bottom. Taking into account the ultrafast change of surface potential, possibly due to the spatial redistribution of nonthermal carriers generated by photoexcitation, an energy width of 0.22 eV was determined as the surface band gap, as well as the surface dispersion properties along three high-symmetry directions.

  17. Pyrometry temperature studies of shocked tin including investigations exploring surface defects, anvil diameter and the integration with emissivity diagnostics

    Science.gov (United States)

    Shenton-Taylor, Caroline; de'Ath, James; Ota, Thomas

    2009-06-01

    Accurate temperature measurement of shock-loaded systems continues to present experimental challenges. With short measurable time durations diagnostic methods are almost exclusively restricted to optical techniques. By preventing full sample pressure unloading, through the use of an anvil, partial release temperature measurements can be deduced from multiple wavelength optical pyrometry. This paper presents our recent studies of tin shocked to 28GPa including investigations exploring surface defects, anvil dimensions and the integration with emissivity diagnostics. The results indicate that a ring groove, 5mm across and with a nominal machined depth of 50 microns, acts to enhance the measured temperature by approximately 150K. Additionally on reducing the LiF anvil diameter from 20mm to 15mm, comparable partial release temperatures were observed. With the anticipated development of multiple anvil target designs, the smaller anvil diameter is desirable. British Crown Copyright 2009/MOD.

  18. Concentrations and distribution of mercury and other heavy metals in surface sediments of the Yatsushiro Sea including Minamata Bay, Japan.

    Science.gov (United States)

    Nakata, Haruhiko; Shimada, Hideaki; Yoshimoto, Maki; Narumi, Rika; Akimoto, Kazumi; Yamashita, Takayuki; Matsunaga, Tomoya; Nishimura, Keisuke; Tanaka, Masakazu; Hiraki, Kenju; Shimasaki, Hideyuki; Takikawa, Kiyoshi

    2008-01-01

    The concentrations and distribution of heavy metals, such as mercury, zinc, copper, lead, and iron in surface sediments from 234 stations of the Yatsushiro Sea including Minamata bay were investigated. High concentrations of mercury were found in sediments from Minamata bay and its vicinity, but the levels decreased gradually with distance from the bay. The concentrations of mercury in sediments decreased gradually from south to north of the Yatsushiro Sea. These imply the lack of movement of mercury from Minamata bay to the northern Yatsushiro Sea. The geographical profiles of zinc and copper were contrary to that found for mercury, indicating the presence of natural and anthropogenic sources of copper and zinc in the northern Yatsushiro Sea.

  19. One-dimensional electron liquid at a surface. Gold nanowires on Ge(001)

    Energy Technology Data Exchange (ETDEWEB)

    Blumenstein, Christian

    2012-09-11

    Self-organized nanowires at semiconductor surfaces offer the unique opportunity to study electrons in reduced dimensions. Notably the dimensionality of the system determines it's electronic properties, beyond the quasiparticle description. In the quasi-one-dimensional (1D) regime with weak lateral coupling between the chains, a Peierls instability can be realized. A nesting condition in the Fermi surface leads to a backfolding of the 1D electron band and thus to an insulating state. It is accompanied by a charge density wave (CDW) in real space that corresponds to the nesting vector. This effect has been claimed to occur in many surface-defined nanowire systems, such as the In chains on Si(111) or the Au reconstructions on the terraced Si(553) and Si(557) surfaces. Therefore a weak coupling between the nanowires in these systems has to be concluded. However theory proposes another state in the perfect 1D limit, which is completely destroyed upon slight coupling to higher dimensions. In this so-called Tomonaga-Luttinger liquid (TLL) state, the quasiparticle description of the Fermi liquid breaks down. Since the interaction between the electrons is enhanced due to the strong confinement, only collective excitations are allowed. This leads to novel effects like spin charge separation, where spin and charge degrees of freedom are decoupled and allowed to travel independently along the 1D-chain. Such rare state has not been realized at a surface until today. This thesis uses a novel approach to realize nanowires with improved confinement by studying the Au reconstructed Ge(001) surface. A new cleaning procedure using piranha solution is presented, in order to prepare a clean and long-range ordered substrate. To ensure optimal growth of the Au nanowires the phase diagram is extensively studied by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The structural elements of the chains are revealed and described in high detail. Remarkably

  20. Effects of electronic relaxation processes on vibrational linewidths of adsorbates on surfaces: The case of CO/Cu(100)

    Science.gov (United States)

    Novko, D.; Alducin, M.; Blanco-Rey, M.; Juaristi, J. I.

    2016-12-01

    We investigate nonadiabatic effects for the vibrational stretch mode of the CO molecule adsorbed on the top site of the Cu(100) surface. By studying the long-wavelength (q ≈0 ) imaginary and real parts of the density functional theory based phonon self-energy due to the electron-phonon coupling Πλ we obtain the phonon linewidth and the frequency renormalization of the CO stretch mode, respectively. To simulate electronic scattering processes that lead to further damping of the phonon modes we include a phenomenological damping in the phonon self-energy, as well as in the single-electron spectral function that enters Πλ, through the momentum distribution function. For the specific case of electron-impurity scattering we explicitly show how this process opens the indirect intraband channel and broadens the linewidth of the CO stretch mode. To emphasize the importance of accounting for electronic scattering processes we compare the phonon linewidths in the clean noninteracting limit (infinite electron lifetime) and when electronic scattering processes are phenomenologically included (finite electron lifetime) with available experimental data. We find that the agreement with experiments is improved in the latter case.

  1. Highly Conductive Transparent and Flexible Electrodes Including Double-Stacked Thin Metal Films for Transparent Flexible Electronics.

    Science.gov (United States)

    Han, Jun Hee; Kim, Do-Hong; Jeong, Eun Gyo; Lee, Tae-Woo; Lee, Myung Keun; Park, Jeong Woo; Lee, Hoseung; Choi, Kyung Cheol

    2017-05-17

    To keep pace with the era of transparent and deformable electronics, electrode functions should be improved. In this paper, an innovative structure is suggested to overcome the trade-off between optical and electrical properties that commonly arises with transparent electrodes. The structure of double-stacked metal films showed high conductivity (flexible enough to withstand 10 000 bending cycles with a 1 mm bending radius. Furthermore, a few μm scale patterning of the electrode was easily implemented by using photolithography, which is widely employed industrially for patterning. Flexible organic light-emitting diodes and a transparent flexible thin-film transistor were successfully fabricated with the proposed electrode. Various practical applications of this electrode to new transparent flexible electronics are expected.

  2. Optical manipulation of ultrafast electron and nuclear motion on metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Petek, Hrvoje

    2009-12-02

    We study the unoccupied electronic structure and dynamics of chemisorbed atoms and molecules on metal surfaces by time resolved two-photon photoemission (TR-2PP). spectroscopy, low temperature scanning tunneling microscopy (LT-STM), and theory. Our research concerns simple atomic adsorbates such as alkali and alkaline earth atoms, which provide fundamentally important models for adsorbate-surface interactions, and more complex adsorbates such as fullerenes on noble metals, which illustrate emergent interfacial properties that derive from intrinsic molecular attributes, and moleculemolecule and molecule-surface interactions. Our goal is to understand how these interactions contribute to formation of the interfacial electronic structure, and how thus formed electronic properties affect interfacial phenomena of importance to energy transduction and storage. Moreover, we explore how the interfacial electronic excitation drives dynamical phenomena such as charge transfer and surface femtochemistry.

  3. High resolution electron energy loss spectroscopy of narrow gap III-V semiconductor surfaces and interfaces

    CERN Document Server

    Veal, T D

    2002-01-01

    The electronic properties of n-type narrow gap III-V semiconductor surfaces and interfaces are investigated using high-resolution electron-energy-loss spectroscopy (HREELS). Changing the incident electron energy, alters the wave-vector transfer parallel to the surface, allowing the probing depth to be varied over typical space-charge layer widths (100 - 2000 A). Semi-classical dielectric theory simulations of the HREEL spectra are performed to extract quantitative information from the probing energy-dependence of the surface plasmon and phonon peaks. The plasma frequency used in the simulations is related to the electron concentration and effective mass using the Kane model of the non-parabolic conduction band. Space-charge layer parameters are obtained by comparing calculated smooth charge profiles with the histogram profiles that are used in the simulations. Complementary experimental techniques are employed to correlate the reconstruction, chemical composition and morphology of the surface with the electro...

  4. Probing the electronic transport on the reconstructed Au/Ge(001 surface

    Directory of Open Access Journals (Sweden)

    Franciszek Krok

    2014-09-01

    Full Text Available By using scanning tunnelling potentiometry we characterized the lateral variation of the electrochemical potential µec on the gold-induced Ge(001-c(8 × 2-Au surface reconstruction while a lateral current flows through the sample. On the reconstruction and across domain boundaries we find that µec shows a constant gradient as a function of the position between the contacts. In addition, nanoscale Au clusters on the surface do not show an electronic coupling to the gold-induced surface reconstruction. In combination with high resolution scanning electron microscopy and transmission electron microscopy, we conclude that an additional transport channel buried about 2 nm underneath the surface represents a major transport channel for electrons.

  5. Surface electronic and structural properties of nanostructured titanium oxide grown by pulsed laser deposition

    NARCIS (Netherlands)

    Fusi, M.; Maccallini, E.; Caruso, T.; Casari, C. S.; Bassi, A. Li; Bottani, C. E.; Rudolf, P.; Prince, K. C.; Agostino, R. G.

    2011-01-01

    Titanium oxide nanostructured thin films synthesized by pulsed laser deposition (PLD) were here characterized with a multi-technique approach to investigate the relation between surface electronic, structural and morphological properties. Depending on the growth parameters, these films present chara

  6. Microstructure evolution during surface alloying of ductile iron and austempered ductile iron by electron beam melting

    Science.gov (United States)

    Gulzar, A.; Akhter, J. I.; Ahmad, M.; Ali, G.; Mahmood, M.; Ajmal, M.

    2009-07-01

    Alloying and microstructural modification of surfaces by electron beam has become popular to tailor the surface properties of materials. Surface modification of as-received ductile iron, Ni-plated ductile iron and Ni-plated austempered ductile iron was carried out by electron beam melting to improve the surface properties. Martensitic structure evolved in the heat affected zone and ledeburite structure was produced in the molten zone of the ductile iron. Microhardness of the melted specimens enhanced considerably as compared to the as-received samples. However the microhardness of melted Ni-plated samples is lower than that of the unplated specimens. X-ray diffraction clearly revealed the formation of an austenite and Fe 3C phases in the electron beam molten zone. The broadening of peaks suggests refinement of the microstructure as well as internal stresses generated during electron beam melting.

  7. Microstructure evolution during surface alloying of ductile iron and austempered ductile iron by electron beam melting

    Energy Technology Data Exchange (ETDEWEB)

    Gulzar, A. [Materials Division, Pakistan Institute of Nuclear Science and Technology, Nilore, Islamabad (Pakistan); Akhter, J.I. [Physics Division, Pakistan Institute of Nuclear Science and Technology, Nilore, Islamabad (Pakistan); Ahmad, M., E-mail: maqomer@yahoo.com [Physics Division, Pakistan Institute of Nuclear Science and Technology, Nilore, Islamabad (Pakistan); Ali, G. [Physics Division, Pakistan Institute of Nuclear Science and Technology, Nilore, Islamabad (Pakistan); Mahmood, M. [Department of Chemical and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences, Islamabad (Pakistan); Ajmal, M. [Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore (Pakistan)

    2009-07-30

    Alloying and microstructural modification of surfaces by electron beam has become popular to tailor the surface properties of materials. Surface modification of as-received ductile iron, Ni-plated ductile iron and Ni-plated austempered ductile iron was carried out by electron beam melting to improve the surface properties. Martensitic structure evolved in the heat affected zone and ledeburite structure was produced in the molten zone of the ductile iron. Microhardness of the melted specimens enhanced considerably as compared to the as-received samples. However the microhardness of melted Ni-plated samples is lower than that of the unplated specimens. X-ray diffraction clearly revealed the formation of an austenite and Fe{sub 3}C phases in the electron beam molten zone. The broadening of peaks suggests refinement of the microstructure as well as internal stresses generated during electron beam melting.

  8. Quantum Nuclear Extension of Electron Nuclear Dynamics on Folded Effective-Potential Surfaces

    DEFF Research Database (Denmark)

    Hall, B.; Deumens, E.; Ohrn, Y.;

    2014-01-01

    A perennial problem in quantum scattering calculations is accurate theoretical treatment of low energy collisions. We propose a method of extracting a folded, nonadiabatic, effective potential energy surface from electron nuclear dynamics (END) trajectories; we then perform nuclear wave packet...

  9. Surface electronic transport measurements: A micro multi-point probe approach

    DEFF Research Database (Denmark)

    Barreto, Lucas

    2014-01-01

    setup, but the terminology used and data analysis were also ameliorated in order to simplify the interpretation of the results. We used the mentioned technique in the following projects: • The electronic transport dimensionality of epitaxial grahene grown on SiC is detected and important physical......This work is mostly focused on the study of electronic transport properties of two-dimensional materials, in particular graphene and topological insulators. To study these, we have improved a unique micro multi-point probe instrument used to perform transport measurements. Not only the experimental...... a direct measurement of the surface electronic transport on a bulk topological insulator. The surface state conductivity and mobility are obtained. Apart from transport properties, we also investigate the atomic structure of the Bi2Se3(111) surface via surface x-ray diraction and low-energy electron...

  10. Guide on the use of low energy electron beams for microbiological decontamination of surfaces

    DEFF Research Database (Denmark)

    Miller, Arne; Helt-Hansen, Jakob; Gondim, Ondina

    This Guide describes the validation and routine monitoring of microbiological decontamination of surfaces by low energy electron beams (100-200 keV). The Guide is mainly based on experience gained in connection with installation of electron beam systems for surface decontamination of pre-steriliz......This Guide describes the validation and routine monitoring of microbiological decontamination of surfaces by low energy electron beams (100-200 keV). The Guide is mainly based on experience gained in connection with installation of electron beam systems for surface decontamination of pre......-sterilized containers at several aseptic filling lines at pharmaceutical manufacturers. Its main emphasis is on the dosimetric measurements that should be carried out for the validation of the decontamination process and on establishing the appropriate effective dose. Other aspects such as use of measurement...... uncertainties and formation of radiation induced by-products are also addressed....

  11. R-matrix calculations for electron-impact excitation of C(+), N(2+), and O(3+) including fine structure

    Science.gov (United States)

    Luo, D.; Pradhan, A. K.

    1990-01-01

    The new R-matrix package for comprehensive close-coupling calculations for electron scattering with the first three ions in the boron isoelectronic sequence, the astrophysically significant C(+), N(2+), and O(3+), is presented. The collision strengths are calculated in the LS coupling approximation, as well as in pair-coupling scheme, for the transitions among the fine-structure sublevels. Calculations are carried out at a large number of energies in order to study the detailed effects of autoionizing resonances.

  12. Strains of Sarcocystis neurona exhibit differences in their surface antigens, including the absence of the major surface antigen SnSAG1.

    Science.gov (United States)

    Howe, Daniel K; Gaji, Rajshekhar Y; Marsh, Antoinette E; Patil, Bhagyashree A; Saville, William J; Lindsay, David S; Dubey, J P; Granstrom, David E

    2008-05-01

    A gene family of surface antigens is expressed by merozoites of Sarcocystis neurona, the primary cause of equine protozoal myeloencephalitis (EPM). These surface proteins, designated SnSAGs, are immunodominant and therefore excellent candidates for development of EPM diagnostics or vaccines. Prior work had identified an EPM isolate lacking the major surface antigen SnSAG1, thus suggesting there may be some diversity in the SnSAGs expressed by different S. neurona isolates. Therefore, a bioinformatic, molecular and immunological study was conducted to assess conservation of the SnSAGs. Examination of an expressed sequence tag (EST) database revealed several notable SnSAG polymorphisms. In particular, the EST information implied that the EPM strain SN4 lacked the major surface antigen SnSAG1. The absence of this surface antigen from the SN4 strain was confirmed by both Western blot and Southern blot. To evaluate SnSAG polymorphisms in the S. neurona population, 14 strains were examined by Western blots using monospecific polyclonal antibodies against the four described SnSAGs. The results of these analyses demonstrated that SnSAG2, SnSAG3, and SnSAG4 are present in all 14 S. neurona strains tested, although some variance in SnSAG4 was observed. Importantly, SnSAG1 was not detected in seven of the strains, which included isolates from four cases of EPM and a case of fatal meningoencephalitis in a sea otter. Genetic analyses by PCR using gene-specific primers confirmed the absence of the SnSAG1 locus in six of these seven strains. Collectively, the data indicated that there is heterogeneity in the surface antigen composition of different S. neurona isolates, which is an important consideration for development of serological tests and prospective vaccines for EPM. Furthermore, the diversity reported herein likely extends to other phenotypes, such as strain virulence, and may have implications for the phylogeny of the various Sarcocystis spp. that undergo sexual stages

  13. Electronic structure, molecular bonding and potential energy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Ruedenberg, K. [Ames Laboratory, IA (United States)

    1993-12-01

    By virtue of the universal validity of the generalized Born-Oppenheimer separation, potential energy surfaces (PES`) represent the central conceptual as well as quantitative entities of chemical physics and provide the basis for the understanding of most physicochemical phenomena in many diverse fields. The research in this group deals with the elucidation of general properties of PES` as well as with the quantitative determination of PES` for concrete systems, in particular pertaining to reactions involving carbon, oxygen, nitrogen and hydrogen molecules.

  14. Dose conversion coefficients for electron exposure of the human eye lens: calculations including a whole body phantom.

    Science.gov (United States)

    Behrens, R

    2013-07-01

    In this work, conversion coefficients from electron fluence to absorbed dose to the eye lens were calculated using Monte Carlo simulations based on a detailed stylised eye model and a very simple but whole body phantom. These data supersede and complement data published earlier based on the simulation of only a single stylised eye. The new data differ from the old ones by not more than 3, 4, 7 and 16 % for angles of radiation incidence of α=0°, 15°, 30° and 45°, respectively, due to the inclusion of the whole body phantom. The data presented in the present work also complement those of a recent report of the International Commission on Radiological Protection (ICRP) (ICRP Publication 116), where conversion coefficients from electron fluence to absorbed dose to the lens of the eye are shown for solely 0°, 180° and isotropic radiation incidence (but for a much broader range of energies). In this article, values are provided for angles of incidence of 0° up to 180° in steps of 15° and for rotational geometry; no systematic deviation was observed from the values given in ICRP Publication 116 for 0° (based on the application of a bare eye) and 180° (based on the application of a voxel whole body phantom). Data are given for monoenergetic electrons from 0.1 up to 10 MeV and for a broad parallel beam geometry in vacuum.

  15. Ab-initio tensorial electronic friction for molecules on metal surfaces: nonadiabatic vibrational relaxation

    CERN Document Server

    Maurer, Reinhard J; Batista, Victor S; Tully, John C

    2016-01-01

    Molecular adsorbates on metal surfaces exchange energy with substrate phonons and low-lying electron-hole pair excitations. In the limit of weak coupling, electron-hole pair excitations can be seen as exerting frictional forces on adsorbates that enhance energy transfer and facilitate vibrational relaxation or hot-electron mediated chemistry. We have recently reported on the relevance of tensorial properties of electronic friction [Phys. Rev. Lett. 116, 217601 (2016)] in dynamics at surfaces. Here we present the underlying implementation of tensorial electronic friction based on Kohn-Sham Density Functional Theory for condensed phase and cluster systems. Using local atomic-orbital basis sets, we calculate nonadiabatic coupling matrix elements and evaluate the full electronic friction tensor in the classical limit. Our approach is numerically stable and robust as shown by a detailed convergence analysis. We furthermore benchmark the accuracy of our approach by calculation of vibrational relaxation rates and li...

  16. Interaction of a Surface Acoustic Wave with a Two-dimensional Electron Gas

    Institute of Scientific and Technical Information of China (English)

    YANG Shi-Jie; ZHAO Hu; YU Yue

    2005-01-01

    When a surface acoustic wave (SAW) propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coefficient is calculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is strongly dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.

  17. Electron band bending and surface sensitivity: X-ray photoelectron spectroscopy of polar GaN surfaces

    Science.gov (United States)

    Bartoš, I.; Romanyuk, O.; Paskova, T.; Jiříček, P.

    2017-10-01

    The role of electron band bending and surface sensitivity in determining the core level binding energies by X-ray photoelectron spectroscopy is investigated. A dominating contribution of surface atomic layers to photoemission intensity is confirmed for normal photoemission. The energy of the photoelectron core level peak does not deviate from core level peak energies of electrons photoemitted from the surface atomic layers of the crystal. The higher surface sensitivity regime, achieved e.g. at off-normal photoelectron detection angle, can be used to study the surface potential barrier in just a few topmost atomic layers. In addition, it is demonstrated that core level binding energy measured by angle-resolved X-ray photoelectron spectroscopy reflect the electron attenuation anisotropy. In particular, core level binding energy changes with emission angle and correlates with the forward focusing directions in a crystal. This effect is demonstrated by measuring the polar angle dependence of Ga 3d core levels on clean GaN(0001) and GaN(000 1 bar) surfaces with a higher and a lower band bending, respectively. The effect is explained by variation of emission depth in a crystal for normal and off-normal photoelectron emission angles.

  18. Hot Electron Photoemission from Plasmonic Nanostructures: The Role of Surface Photoemission and Transition Absorption

    DEFF Research Database (Denmark)

    Babicheva, Viktoriia; Zhukovsky, Sergei; Ikhsanov, Renat Sh;

    2015-01-01

    We study mechanisms of photoemission of hot electrons from plasmonic nanoparticles. We analyze the contribution of "transition absorption", i.e., loss of energy of electrons passing through the boundary between different materials, to the surface mechanism of photoemission. We calculate photoemis...

  19. Secondary electron yield from stainless steel surface coated with titanium nitride

    Science.gov (United States)

    Orlov, O. S.; Meshkov, I. N.; Rudakov, A. Yu.; Philippov, A. V.

    2014-09-01

    The experiment on measurement of secondary electron yield from surface of a stainless steel Kh189 sample covered with titanium nitride is performed at stand "Recuperator". This work is related to known problem of electron clouds formation in a vacuum chamber by a propagating charge particle beam. An original method of secondary electron yield measurement was developed in this experiment. The obtained results allow one to estimate efficiency of coating nitride titanium.

  20. Reduced Heat Flux Through Preferential Surface Reactions Leading to Vibrationally and Electronically Excited Product States

    Science.gov (United States)

    2016-03-04

    AFRL-AFOSR-VA-TR-2016-0124 Reduced Heat Flux Through Preferential Surface Reactions Leading to Vibrationally and Electronically Excited Product...Reactions Leading to Vibrationally and Electronically Excited Product States 5a. CONTRACT NUMBER FA9550-12-1-0486 5b. GRANT NUMBER 5c. PROGRAM... Leading to Vibrationally and Electronically Excited Product States FINAL TECHNICAL REPORT: Grant #FA9550-12-1-0486 2013 Basic Research Initiative (BRI

  1. The surface magnetization study of Cr2O3 by spin polarized low energy electron microscopy

    Science.gov (United States)

    Cao, Shi; Wu, Ning; Zhang, Xin; N'diaye, Alpha; Chen, Gong; Schmid, Andreas; Echtenkamp, Will; Lauter, Valeria; Binek, Christian; Dowben, Peter

    2014-03-01

    The boundary magnetization at the surface of a Cr2O3 single crystal has been demonstrated by using spin-polarized low-energy electron microscopy (SPLEEM), indicating net surface spin polarization. This work shows that the placement of Cr2O3 single crystal in the single domain state, will result in net Cr2O3 spin polarization at the boundary, even in the presence of a gold overlayer. There are indications that the spin-polarized low-energy electron microscopy (SPLEEM) contrast for the two polarizations states is different. In addition, the boundary magnetization protected by the symmetry exists despite of the surface roughness/softness which was studied by the non-spin neutron reflectometry and low energy electron diffraction. Unoccupied surface oxygen sites and chromium sites are possible mechanism contributing to the surface ``softness,'' which will be discussed.

  2. Electronic transport at semiconductor surfaces - from point-contact transistor to micro-four-point probes

    DEFF Research Database (Denmark)

    Hasegawa, S.; Grey, Francois

    2002-01-01

    show that this type of conduction is measurable using new types of experimental probes, such as the multi-tip scanning tunnelling microscope and the micro-four-point probe. The resulting electronic transport properties are intriguing, and suggest that semiconductor surfaces should be considered......The electrical properties of semiconductor surfaces have played a decisive role in one of the most important discoveries of the last century, transistors. In the 1940s, the concept of surface states-new electron energy levels characteristic of the surface atoms-was instrumental in the fabrication...... of the first point-contact transistors, and led to the successful fabrication of field-effect transistors. However, to this day, one property of semiconductor surface states remains poorly understood, both theoretically and experimentally. That is the conduction of electrons or holes directly through...

  3. MONTE CARLO SIMULATION STUDY OF SURFACE ELECTRONIC EXCITATION OF NOBLE METALS

    Institute of Scientific and Technical Information of China (English)

    H.M. Li; Z.J. Ding; Q.R. Pu; Z.M. Zhang

    2002-01-01

    In this work we present a numerical simulation of REELS-spectrum for noble metals,Au and Ag. The calculation is based on an electron-surface inelastic scattering modelpreviously developed. The differential inelastic cross section is obtained fron an inho-mogeneous electron self-energy in the surface region, which provides full informationof the dependency of the total and differential cross section on the kinetic energy,the distance from the surface and the moving direction of electrons, accommodatingthe formulation to the practical situation in surface electron spectroscopes. A novelMonte Carlo simulation code of electron interaction with a surface incorporating thelocal scattering mean free path has been developed. The comparison of the simulatedREELS-spectra with the experimental measurements shows a remarkable agreement onthe spectrum shape, which then confirms that the present model for electron-surfaceinelastic .scattering is quite reasonable. The simulation has further shown the compo.nent to surface excitation due to the individual scattering processes along trajectorypart, i.e., the loss in vacuum before reflection, the loss in vacuum after reflection andloss in metal events.

  4. Tuning the surface electronic structure of a Pt3Ti(111) electro catalyst

    Science.gov (United States)

    Paßens, M.; Caciuc, V.; Atodiresei, N.; Moors, M.; Blügel, S.; Waser, R.; Karthäuser, S.

    2016-07-01

    Increasing the efficiency and stability of bimetallic electro catalysts is particularly important for future clean energy technologies. However, the relationship between the surface termination of these alloys and their catalytic activity is poorly understood. Therefore, we report on fundamental UHV-SPM, LEED, and DFT calculations of the Pt3Ti(111) single crystal surface. Using voltage dependent imaging the surface termination of Pt3Ti(111) was studied with atomic resolution. Combining these images with simulated STM maps based on ab initio DFT calculations allowed us to identify the three upper layers of the Pt3Ti(111) single crystal and their influence upon the surface electronic structure. Our results show that small changes in the composition of the second and third atomic layer are of significant influence upon the surface electronic structure of the Pt3Ti electro catalyst. Furthermore, we provide relevant insights into the dependence of the surface termination on the preparation conditions.Increasing the efficiency and stability of bimetallic electro catalysts is particularly important for future clean energy technologies. However, the relationship between the surface termination of these alloys and their catalytic activity is poorly understood. Therefore, we report on fundamental UHV-SPM, LEED, and DFT calculations of the Pt3Ti(111) single crystal surface. Using voltage dependent imaging the surface termination of Pt3Ti(111) was studied with atomic resolution. Combining these images with simulated STM maps based on ab initio DFT calculations allowed us to identify the three upper layers of the Pt3Ti(111) single crystal and their influence upon the surface electronic structure. Our results show that small changes in the composition of the second and third atomic layer are of significant influence upon the surface electronic structure of the Pt3Ti electro catalyst. Furthermore, we provide relevant insights into the dependence of the surface termination on the

  5. The erosive potential of soft drinks on enamel surface substrate: an in vitro scanning electron microscopy investigation.

    Science.gov (United States)

    Owens, Barry M; Kitchens, Michael

    2007-11-01

    Using scanning electron and light microscopy, this study qualitatively evaluated the erosive potential of carbonated cola beverages as well as sports and high-energy drinks on enamel surface substrate. Beverages used in this study included: Coca Cola Classic, Diet Coke, Gatorade sports drink, Red Bull high-energy drink, and tap water (control). Extracted human permanent molars free of hypocalcification and/or caries were used in this study. The coronal portion of each tooth was removed and sectioned longitudinally from the buccal to the lingual surface. The crown sections were embedded in acrylic resin, leaving the enamel surfaces exposed. Following finishing and polishing of all surfaces, one side was covered with red nail varnish while the remaining side was exposed to individual beverage immersion for 14 days, 24 hours per day, at 37 degrees C. The specimens were evaluated for enamel surface changes using scanning electron and light microscopy. Enamel specimens exhibited visual surface changes following immersion in the test beverages with Red Bull and Gatorade revealing the most striking surface morphological changes. Specimens subjected to Coca Cola Classic and Diet Coke immersion also displayed irregular post-treatment surface morphology. As verified by microscopic evaluation, all test beverages displayed enamel dissolution in the following order: Red Bull>Gatorade>Coca-Cola Classic>Diet Coke.

  6. Ionic liquids influence on the surface properties of electron beam irradiated wood

    Energy Technology Data Exchange (ETDEWEB)

    Croitoru, Catalin [“Transilvania” University of Brasov, Product Design and Environment Department, 29 Eroilor Str., 500036, Brasov (Romania); Patachia, Silvia, E-mail: st.patachia@unitbv.ro [“Transilvania” University of Brasov, Product Design and Environment Department, 29 Eroilor Str., 500036, Brasov (Romania); Doroftei, Florica; Parparita, Elena; Vasile, Cornelia [“Petru Poni” Institute of Macromolecular Chemistry, Physical Chemistry of Polymers Department, 41A Gr. Ghica Voda Alley, Iasi (Romania)

    2014-09-30

    Highlights: • Wood veneers impregnated with three imidazolium-based ionic liquids and irradiated with electron beam were studied by FTIR-ATR, SEM/EDX, AFM, contact angle and image analysis. • ILs preserve the surface properties of the wood (surface energy, roughness, color) upon irradiation, in comparison with the reference wood, but the surface composition is changed by treatment with IL-s, mainly with 1-butyl-3-methylimidazolium tetrafluoroborate. • Under electron beam irradiation covalent bonding of the imidazolium moiety to wood determines a higher resistance to water penetration and spreading on the surface. - Abstract: In this paper, the influence of three imidazolium-based ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate and 1-hexyl-3-methylimidazolium chloride) on the structure and surface properties of sycamore maple (Acer pseudoplatanus) veneers submitted to electron beam irradiation with a dose of 50 kGy has been studied by using Fourier transform infrared spectroscopy, as well as image, scanning electron microscopy/SEM/EDX, atomic force microscopy and contact angle analysis. The experimental results have proven that the studied ionic liquids determine a better preservation of the structural features of wood (cellulose crystallinity index and lignin concentration on the surface) as well as some of surface properties such as surface energy, roughness, color upon irradiation with electron beam, in comparison with the reference wood, but surface composition is changed by treatment with imidazolium-based ionic liquids mainly with 1-butyl-3-methylimidazolium tetrafluoroborate. Also, under electron beam irradiation covalent bonding of the imidazolium moiety to wood determines a higher resistance to water penetration and spreading on the surface.

  7. MIS hot electron devices for enhancement of surface reactivity by hot electrons

    DEFF Research Database (Denmark)

    Thomsen, Lasse Bjørchmar

    to be an important energy loss center for the electrons tunneling through the oxide lowering the emission e±ciency of a factor of 10 for a 1 nm Ti layer thickness. Electron emission is observed under ambient pressure conditions and in up to 2 bars of Ar. 2 bar Ar decrease the emission current by an order...... is monitored using the calibrated resistance of the metal layer. The MIS hot electron emitters are cleaned in-situ in a background pressure of 3 £ 10¡7 mbar O2. Thermal desorption experiments with labeled CO are carried out with a reproducibility of 7%. The detection limit of labeled CO for the mass...

  8. Experimental investigations into secondary electron-electron emission from the surface of vacuum chambers

    Science.gov (United States)

    Meshkov, I. N.; Rudakov, A. Yu.

    2012-07-01

    An experiment on measuring the secondary electron yield (SEY) of samples coated with titanium nitride (TiN2) is in progress at the Recuperator test bench at the Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research. This work is related the problem of electron-cloud formation in the vacuum chambers of accelerators and is of practical importance for the NICA project. The results of the experiment on the SEY measurement will make it possible to choose the most appropriate material for coating the vacuum chamber. In this experiment samples of stainless steel with titanium nitride coating and without any coating are compared.

  9. Snell's law for surface electrons: Refraction of an electron gas imaged in real space

    OpenAIRE

    Repp, Jascha; Meyer, Gerhard; Rieder, Karl-Heinz

    2003-01-01

    On NaCl(100)/Cu(111) an interface state band is observed that descends from the surface-state band of the clean copper surface. This band exhibits a Moire-pattern-induced one-dimensional band gap, which is accompanied by strong standing-wave patterns, as revealed in low-temperature scanning tunneling microscopy images. At NaCl island step edges, one can directly see the refraction of these standing waves, which obey Snell's refraction law.

  10. Snell's law for surface electrons: refraction of an electron gas imaged in real space.

    Science.gov (United States)

    Repp, Jascha; Meyer, Gerhard; Rieder, Karl-Heinz

    2004-01-23

    On NaCl(100)/Cu(111) an interface state band is observed that descends from the surface-state band of the clean copper surface. This band exhibits a Moiré-pattern-induced one-dimensional band gap, which is accompanied by strong standing-wave patterns, as revealed in low-temperature scanning tunneling microscopy images. At NaCl island step edges, one can directly see the refraction of these standing waves, which obey Snell's refraction law.

  11. Micro-Shaping of Nanopatterned Surfaces by Electron Beam Irradiation

    Directory of Open Access Journals (Sweden)

    Carlos Angulo Barrios

    2016-04-01

    Full Text Available We show that planar nanopatterned thin films on standard polycarbonate (PC compact discs (CD can be micro-shaped in a non-contact manner via direct e-beam exposure. The shape of the film can be controlled by proper selection of the e-beam parameters. As an example of application, we demonstrate a two-dimensional (2D array of micro-lenses/reservoirs conformally covered by an Al 2D nanohole array (NHA film on a PC CD substrate. It is also shown that such a curvilinear Al NHA layer can be easily transferred onto a flexible polymeric support. The presented technique provides a new tool for creating lab-on-CD architectures and developing multifunctional (flexible non-planar nanostructured films and surfaces.

  12. Study of surface leakage current of AlGaN/GaN high electron mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Chen, YongHe; Zhang, Kai; Cao, MengYi; Zhao, ShengLei; Zhang, JinCheng; Hao, Yue, E-mail: yhao@xidian.edu.cn [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China); Ma, XiaoHua, E-mail: xhma@xidian.edu.cn [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China); School of Advanced Materials and Nanotechnology, Xidian University, Xi' an 710071 (China)

    2014-04-14

    Temperature-dependent surface current measurements were performed to analyze the mechanism of surface conductance of AlGaN/GaN channel high-electron-mobility transistors by utilizing process-optimized double gate structures. Different temperatures and electric field dependence have been found in surface current measurements. At low electric field, the mechanism of surface conductance is considered to be two-dimensional variable range hopping. At elevated electric field, the Frenkel–Poole trap assisted emission governs the main surface electrons transportation. The extracted energy barrier height of electrons emitting from trapped state near Fermi energy level into a threading dislocations-related continuum state is 0.38 eV. SiN passivation reduces the surface leakage current by two order of magnitude and nearly 4 orders of magnitude at low and high electric fields, respectively. SiN also suppresses the Frenkel–Poole conductance at high temperature by improving the surface states of AlGaN/GaN. A surface treatment process has been introduced to further suppress the surface leakage current at high temperature and high field, which results in a decrease in surface current of almost 3 orders of magnitude at 476 K.

  13. Towards hot electron mediated charge exchange in hyperthermal energy ion-surface interactions

    DEFF Research Database (Denmark)

    Ray, M. P.; Lake, R. E.; Thomsen, Lasse Bjørchmar;

    2010-01-01

    electrons useful for driving chemical reactions at surfaces. Using the binary collision approximation and a nonadiabatic model that takes into account the time-varying nature of the ion–surface interaction, the energy loss of the ions is reproduced. The energy loss for Na + ions incident on the devices...

  14. Frictional and bone ingrowth properties of engineered surface topographies produced by electron beam technology

    NARCIS (Netherlands)

    Biemond, J.E.; Aquarius, R.J.M.; Verdonschot, N.J.J.; Buma, P.

    2011-01-01

    BACKGROUND: Electron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants. METHODS: The friction coefficients of two newly developed E-beam produced surface topographies were in vitro compared with sandblasted E-beam and titanium

  15. Frictional and bone ingrowth properties of engineered surface topographies produced by electron beam technology

    NARCIS (Netherlands)

    Biemond, J. Elizabeth; Aquarius, Rene; Verdonschot, Nicolaas Jacobus Joseph; Buma, Pieter

    2011-01-01

    Background Electron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants. Methods The friction coefficients of two newly developed E-beam produced surface topographies were in vitro compared with sandblasted E-beam and titanium

  16. Surface sensitivity effects with local probe scanning Auger–scanning electron microscopy

    NARCIS (Netherlands)

    Agterveld, D.T.L. van; Palasantzas, G.; Hosson, J.Th.M. De

    1999-01-01

    This letter concentrates on a quantitative description of surface roughness effects on Auger peak-line profiles for pure and alloyed specimens. The nanometer lateral electron probe size of the order of 10 nm yielded peak-line profiles that capture surface topology variations down to nanometer-length

  17. Preface: Special Topic Section on Advanced Electronic Structure Methods for Solids and Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Michaelides, Angelos, E-mail: angelos.michaelides@ucl.ac.uk [London Centre for Nanotechnology and Department of Chemistry, University College London, London (United Kingdom); Martinez, Todd J. [Department of Chemistry and the PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Alavi, Ali [Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany and Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom); Kresse, Georg [Faculty of Physics and Center for Computational Materials Science, Department of Physics, University of Vienna, Sensengasse 8/12, A-1090 Vienna (Austria); Manby, Frederick R. [Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS (United Kingdom)

    2015-09-14

    This Special Topic section on Advanced Electronic Structure Methods for Solids and Surfaces contains a collection of research papers that showcase recent advances in the high accuracy prediction of materials and surface properties. It provides a timely snapshot of a growing field that is of broad importance to chemistry, physics, and materials science.

  18. Direct observation of surface reconstruction and termination on a complex metal oxide catalyst by electron microscopy

    KAUST Repository

    Zhu, Yihan

    2012-03-19

    On the surface: The surface reconstruction of an MoVTeO complex metal oxide catalyst was observed directly by various electron microscopic techniques and the results explain the puzzling catalytic behavior. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Potential and Kinetic Electron Emissions from HOPG Surface Irradiated by Highly Charged Xenon and Neon Ions

    Institute of Scientific and Technical Information of China (English)

    WANG Yu-Yu; ZHAO Yong-Tao; SUN Jian-Rong; LI De-Hui; QAYYUM Abdul; LI Jin-Yu; WANG Ping-Zhi; XIAO Guo-Qing

    2011-01-01

    Highly charged 129 Xeq+ (q =10-30) and 40Neq+ (q =4-8) ion-induced secondary electron emissions on the surface of highly oriented pyrolytic graphite (HOPG) are reported. The total secondary electron yield is measured as a function of the potential energy of incident ions. The experimental data are used to separate contributions of kinetic and potential electron yields. Our results show that about 4.5% and 13.2% of ion's potential energies are consumed in potential electron emission due to different Xeq+-HOPG and Neq+-HOPG combinations. A simple formula is introduced to estimate the fraction of ion's potential energy for potential electron emission.%@@ Highly charged 129 Xeq+(q =10-30) and 40Neq+(q =4-8) ion-induced secondary electron emissions on the surface of highly oriented pyrolytic graphite(HOPG) are reported.The total secondary electron yield is measured as a function of the potential energy of incident ions.The experimental data are used to separate contributions of kinetic and potential electron yields.Our results show that about 4.5% and 13.2% of ion's potential energies are consumed in potential electron emission due to different Xeq+-HOPG and Neq+-HOPG combinations.A simple formula is introduced to estimate the fraction of ion's potential energy for potential electron emission.

  20. Quantum corrected Langevin dynamics for adsorbates on metal surfaces interacting with hot electrons

    DEFF Research Database (Denmark)

    Olsen, Thomas; Schiøtz, Jakob

    2010-01-01

    quantum mechanical probabilities from the classical phase space distributions resulting from the dynamics. At short time scales, classical and quasiclassical initial conditions lead to wrong results and only correctly quantized initial conditions give a close agreement with an inherently quantum......We investigate the importance of including quantized initial conditions in Langevin dynamics for adsorbates interacting with a thermal reservoir of electrons. For quadratic potentials the time evolution is exactly described by a classical Langevin equation and it is shown how to rigorously obtain...... mechanical master equation approach. With CO on Cu(100) as an example, we demonstrate the effect for a system with ab initio frictional tensor and potential energy surfaces and show that quantizing the initial conditions can have a large impact on both the desorption probability and the distribution...

  1. Electronic tongue-based discrimination of Korean rice wines (makgeolli) including prediction of sensory evaluation and instrumental measurements.

    Science.gov (United States)

    Kang, Bo-Sik; Lee, Jang-Eun; Park, Hyun-Jin

    2014-05-15

    A commercial electronic tongue was used to discriminate Korean rice wines (makgeolli) brewed from nine cultivars of rice with different amino acid and fatty acid compositions. The E-tongue was applied to establish prediction models with sensory evaluation or LC-MS/MS by partial least squares regression (PLSR). All makgeollis were classified into three groups by principal components analysis, and the separation pattern was affected by rice qualities and yeast fermentation. Makgeolli taste changed from the complicated comprising sweetness, saltiness, and umami to the uncomplicated, such as bitterness and then, sourness, with a decrease of amino acids and fatty acids in the rice. The quantitative correlation between E-tongue and sensory scores or LC-MS/MS by PLSR demonstrated that E-tongue could well predict most of the sensory attributes with relatively acceptable r(2), except for bitterness, but could not predict most of the chemical compounds responsible for taste attributes, except for ribose, lactate, succinate, and tryptophan.

  2. Electron field emission from nanostructured surfaces of GaN and AlGaN

    Energy Technology Data Exchange (ETDEWEB)

    Evtukh, A.; Litovchenko, V.; Semenenko, M.; Gorbanyuk, T.; Grygoriev, A. [Institute of Semiconductor Physics, 41 prospekt Nauki, 03028 Kiev (Ukraine); Yilmazoglu, O.; Hartnagel, H.; Pavlidis, D. [Technische Universitaet Darmstadt, Institut fuer Hochfrequenztechnik, Merckstr. 25, 64283 Darmstadt (Germany)

    2008-07-01

    The possibility of high frequency electromagnetic wave generation by field emission based devices has great interest. The wide bandgap materials GaN and AlGaN are very promising for these applications due to low electron affinity and the existence of satellite valleys in conduction band. The results of investigations of the peculiarities of electron field emission from nanostructured surfaces of GaN and AlGaN are presented. Multilayer GaN and AlGaN structures with various levels of layer doping on sapphire and bulk GaN substrates were used as initial wafers. The surface of the upper layers was nanostructured by photoelectrochemical etching in water solution of KOH. Intensive electron field emission into vacuum was observed and explained by low electron affinity and electric field enhancement on surface nanowires. A decrease of the slope in the Fowler-Nordheim characteristics was revealed. The changing slope suggests a lowering of effective work function. It is caused by electron heating and transfer into an upper satellite valley with lower electron affinity. A theory was developed for the observed phenomena and interpretation of results. It is based on electron intervalley transition upon heating and on energy band reconstruction of the surface of the nanowires due to quantum size-confinement effect. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Effective Model for Massless Dirac Electrons on a Surface of Weak Topological Insulators

    Science.gov (United States)

    Arita, Takashi; Takane, Yositake

    2014-12-01

    In a typical situation, gapless surface states of a three-dimensional (3D) weak topological insulator (WTI) appear only on the sides, leaving the top and bottom surfaces gapped. To describe massless Dirac electrons emergent on such side surfaces of a WTI, a two-dimensional (2D) model consisting of a series of one-dimensional helical channels is usually employed. However, an explicit derivation of such a model from a 3D bulk Hamiltonian has been lacking. Here, we explicitly derive an effective 2D model for the WTI surface states starting from the Wilson-Dirac Hamiltonian for the bulk WTI and establish a firm basis for the hitherto hypothesized 2D model. We show that the resulting 2D model accurately reproduces the excitation spectrum of surface Dirac electrons determined by the 3D model. We also show that the 2D model is applicable to a side surface with atomic steps.

  4. Excitation of surface and volume plasmons in metal nanocluster by fast electrons

    CERN Document Server

    Gildenburg, V B; Pavlichenko, I A

    2015-01-01

    Surface and volume plasmons excited in a metal cluster by moving electron and corresponding inelastic scattering spectra are studied based on the hydrodynamic approach. Along with the bulk losses traditionally taken into account, the surface and radiative ones are also considered as the physical mechanisms responsible for the plasmon damping. The second and third mechanisms are found to be essential for the surface plasmons and depend very differently on the multipole mode order. The differential equations are obtained which describe the temporal evolution of every particular mode as that one of a linear oscillator excited by the given external force, and the electron energy loss spectra are calculated. The changes in spectrum shape with the impact parameter and with the electron passage time are analyzed and found to be in good enough agreement with the data of scanning transmission electron microscopy (STEM) experiments. It is shown that, in the general case, a pronounced contribution to the formation of th...

  5. Effect of dielectric coating on the electron work function and the surface stress of a metal

    Science.gov (United States)

    Babich, A. V.; Pogosov, V. V.

    2009-08-01

    The electron work function, contact potential difference, and surface stress of the elastically deformed faces of the metal covered by a dielectric are calculated by using the Kohn-Sham method and stabilized jellium model. Our calculations demonstrate the opposite deformation dependencies of the work function and contact potential difference. Dielectric coating leads to a negative change in the work function and a positive change in the contact potential difference. It is shown that the measurements of the contact potential difference of a deformed face by the Kelvin method give only the change in the value of the one-electron effective potential in the plane of a virtual image behind the surface, rather than the value of the electron work function. The obtained values of the electron work function and surface stress for Al, Au, Cu, and Zn are in agreement with the results of experiments for polycrystals.

  6. Chemical, electronic, and magnetic structure of LaFeCoSi alloy: Surface and bulk properties

    Energy Technology Data Exchange (ETDEWEB)

    Lollobrigida, V. [Dipartimento di Scienze, Università Roma Tre, I-00146 Rome (Italy); Dipartimento di Matematica e Fisica, Università Roma Tre, I-00146 Rome (Italy); Basso, V.; Kuepferling, M.; Coïsson, M.; Olivetti, E. S.; Celegato, F. [Istituto Nazionale di Ricerca Metrologica (INRIM), I-10135 Torino (Italy); Borgatti, F. [CNR, Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), I-40129 Bologna (Italy); Torelli, P.; Panaccione, G. [CNR, Istituto Officina dei Materiali (IOM), Lab. TASC, I-34149 Trieste (Italy); Tortora, L. [Laboratorio di Analisi di Superficie, Dipartimento di Matematica e Fisica, Università Roma Tre, I-00146 Rome (Italy); Dipartimento di Ingegneria Meccanica, Università Tor Vergata, I-00133 Rome (Italy); Stefani, G.; Offi, F. [Dipartimento di Scienze, Università Roma Tre, I-00146 Rome (Italy)

    2014-05-28

    We investigate the chemical, electronic, and magnetic structure of the magnetocaloric LaFeCoSi compound with bulk and surface sensitive techniques. We put in evidence that the surface retains a soft ferromagnetic behavior at temperatures higher than the Curie temperature of the bulk due to the presence of Fe clusters at the surface only. This peculiar magnetic surface effect is attributed to the exchange interaction between the ferromagnetic Fe clusters located at the surface and the bulk magnetocaloric alloy, and it is used here to monitor the magnetic properties of the alloy itself.

  7. Primary role of electron work function for evaluation of nanostructured titania implant surface against bacterial infection

    Energy Technology Data Exchange (ETDEWEB)

    Golda-Cepa, M., E-mail: golda@chemia.uj.edu.pl [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland); Syrek, K. [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland); Brzychczy-Wloch, M. [Department of Bacteriology, Microbial Ecology and Parasitology, Jagiellonian University Medical College, Czysta 18, 31-121 Krakow (Poland); Sulka, G.D. [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland); Kotarba, A., E-mail: kotarba@chemia.uj.edu.pl [Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow (Poland)

    2016-09-01

    The electron work function as an essential descriptor for the evaluation of metal implant surfaces against bacterial infection is identified for the first time. Its validity is demonstrated on Staphylococcus aureus adhesion to nanostructured titania surfaces. The established correlation: work function–bacteria adhesion is of general importance since it can be used for direct evaluation of any electrically conductive implant surfaces. - Highlights: • The correlation between work function and bacteria adhesion was discovered. • The discovered correlation is rationalized in terms of electrostatic bacteria–surface repulsion. • The results provide basis for the simple evaluation of implant surfaces against infection.

  8. Scanning electron microscopy study of protein immobilized on SIO2 Sol-gel surfaces

    Directory of Open Access Journals (Sweden)

    O.B.G. Assis

    2003-09-01

    Full Text Available Uniform attachment of enzymes to solid surfaces is essential in the development of bio and optical sensor devices. Immobilization by adsorption according to hydrophilic or hydrophobic nature is dependent on the charges and defects of the support surfaces. Sol-gel SiO2 densified glass surfaces, frequently used as supports for protein immobilization, are evaluated via scanning electron microscopy. The model protein is globular enzyme lysozyme, deposited by adsorption on functionalized surfaces. Formation of a protein layer is confirmed by FTIR spectroscopy, and the SEM images suggest discontinuous adsorption in areas where cracks predominate on the glass surface.

  9. The Helium Field Effect Transistor (I): Storing Surface State Electrons on Helium Films

    Science.gov (United States)

    Ashari, M.; Rees, D. G.; Kono, K.; Scheer, E.; Leiderer, P.

    2012-04-01

    We present investigations of surface state electrons on liquid helium films in confined geometry, using a suitable substrate structure microfabricated on a silicon wafer, similar to a Field Effect Transistor (FET). The sample has a source and drain region, separated by a gate structure, which consists of two gold electrodes with a narrow gap (channel) through which the transport of the surface state electrons takes place. The sample is illuminated to provide a sufficient number of free carriers in the silicon substrate, such that a well-defined potential distribution is achieved. The eventual goal of these experiments is to study the electron transport through a narrow channel in the various states of the phase diagram of the 2D electron system. In the present work we focus on storing the electrons in the source area of the FET, and investigate the spatial distribution of these electrons. It is shown that under the influence of a potential gradient in the silicon substrate the electrons accumulate in front of the potential barrier of the gate. The electron distribution, governed by Coulomb repulsion and by the substrate potential, is determined experimentally. The result is found to be in good agreement with a parallel-plate capacitor model of the system, developed with the aid of a finite element calculation of the surface potential profile of the device.

  10. Developing the Surface Chemistry of Transparent Butyl Rubber for Impermeable Stretchable Electronics.

    Science.gov (United States)

    Vohra, Akhil; Carmichael, R Stephen; Carmichael, Tricia Breen

    2016-10-11

    Transparent butyl rubber is a new elastomer that has the potential to revolutionize stretchable electronics due to its intrinsically low gas permeability. Encapsulating organic electronic materials and devices with transparent butyl rubber protects them from problematic degradation due to oxygen and moisture, preventing premature device failure and enabling the fabrication of stretchable organic electronic devices with practical lifetimes. Here, we report a methodology to alter the surface chemistry of transparent butyl rubber to advance this material from acting as a simple device encapsulant to functioning as a substrate primed for direct device fabrication on its surface. We demonstrate a combination of plasma and chemical treatment to deposit a hydrophilic silicate layer on the transparent butyl rubber surface to create a new layered composite that combines Si-OH surface chemistry with the favorable gas-barrier properties of bulk transparent butyl rubber. We demonstrate that these surface Si-OH groups react with organosilanes to form self-assembled monolayers necessary for the deposition of electronic materials, and furthermore demonstrate the fabrication of stretchable gold wires using nanotransfer printing of gold films onto transparent butyl rubber modified with a thiol-terminated self-assembled monolayer. The surface modification of transparent butyl rubber establishes this material as an important new elastomer for stretchable electronics and opens the way to robust, stretchable devices.

  11. Effect of Autoclave Cycles on Surface Characteristics of S-File Evaluated by Scanning Electron Microscopy

    OpenAIRE

    Razavian, Hamid; Iranmanesh, Pedram; Mojtahedi, Hamid; Nazeri, Rahman

    2015-01-01

    Introduction: Presence of surface defects in endodontic instruments can lead to unwanted complications such as instrument fracture and incomplete preparation of the canal. The current study was conducted to evaluate the effect of autoclave cycles on surface characteristics of S-File by scanning electron microscopy (SEM). Methods and Materials: In this experimental study, 17 brand new S-Files (#30) were used. The surface characteristics of the files were examined in four steps (without autocla...

  12. Structures, electronic properties and stability phase diagrams for copper(I/II) bromide surfaces.

    Science.gov (United States)

    Altarawneh, Mohammednoor; Marashdeh, Ali; Dlugogorski, Bogdan Z

    2015-04-14

    This study presents a comprehensive periodic slab DFT investigation into structures, electronic properties and thermodynamic stability of all plausible terminations of CuBr and CuBr2 surfaces. We first estimate lattice constants, formation and cohesive energies for the two bulk copper bromides before proceeding to analyse geometrical and electronic features of CuBr and CuBr2 configurations. Surface geometries exhibit, to a large extent, corresponding bulk structures. Nevertheless, certain CuBr2 surfaces experience a downward displacement of the topmost Cu-containing layers. We plot total and projected density of states for bulk and surface geometries of these two copper bromides and calculate their associated Bader's electronic charges. Electronic structure analysis for the bulk and surfaces of these two copper bromides show that CuBr bulk and its most stable surface (CuBr(001)_Br) do not exhibit any metallic character, whereas CuBr2 bulk and its most stable surface (CuBr2(001)_Br) both exhibit metallic characters. The formalism of the ab initio atomistic thermodynamics affords the construction of energy phase diagrams. We predict that the CuBr(001) surface, truncated with Br atoms, is the most stable structure among the considered CuBr slabs at all physically meaningful ranges of the chemical potential of bromine. This surface resembles a c(2 × 2)-bromine sheet that was characterised experimentally from initial interaction of Br2 with a Cu(100) surface. We find that surfaces terminated with the electronegative bromine atoms, if accompanied by significant relaxation, tend to be more stable. Calculated surface energies predict the shapes of CuBr and CuBr2 nanoparticles as the chemical potential of bromine changes.

  13. Effect of Autoclave Cycles on Surface Characteristics of S-File Evaluated by Scanning Electron Microscopy

    OpenAIRE

    Razavian, Hamid; Iranmanesh, Pedram; Mojtahedi, Hamid; Nazeri, Rahman

    2015-01-01

    Introduction: Presence of surface defects in endodontic instruments can lead to unwanted complications such as instrument fracture and incomplete preparation of the canal. The current study was conducted to evaluate the effect of autoclave cycles on surface characteristics of S-File by scanning electron microscopy (SEM). Methods and Materials: In this experimental study, 17 brand new S-Files (#30) were used. The surface characteristics of the files were examined in four steps (without autocla...

  14. Implementation of variable time step stochastic dynamics for electronically inelastic gas-surface collisions

    Science.gov (United States)

    Garrett, Bruce C.; Swaminathan, P. K.; Murthy, C. S.; Redmon, Michael J.

    1987-01-01

    A variable time step algorithm has been implemented for solving the stochastic equations of motion for gas-surface collisions. It has been tested for a simple model of electronically inelastic collisions with an insulator surface in which the phonon manifold acts as a heat bath and electronic states are localized. In addition to reproducing the accurate nuclear dynamics of the surface atoms, numerical calculations have shown the algorithm to yield accurate ensemble averages of physical observables such as electronic transition probabilities and total energy loss of the gas atom to the surface. This new algorithm offers a gain in efficieny of up to an order of magnitude compared to fixed time step integration.

  15. Sulfur passivation of surface electrons in highly Mg-doped InN

    Energy Technology Data Exchange (ETDEWEB)

    Linhart, W. M.; Veal, T. D. [Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 4ZF (United Kingdom); Chai, J. [Department of Electrical and Computer Engineering, University of Canterbury, Christchurch 8140 (New Zealand); McConville, C. F. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Durbin, S. M. [Department of Electrical and Computer Engineering, University of Canterbury, Christchurch 8140 (New Zealand); Department of Electrical and Computer Engineering, Western Michigan University, Kalamazoo, Michigan 49008 (United States)

    2013-09-14

    Electron accumulation with a sheet density greater than 10{sup 13} cm{sup −2} usually occurs at InN surfaces. Here, the effects of treatment with ammonium sulfide ((NH{sub 4}){sub 2}S{sub x}) on the surface electronic properties of highly Mg-doped InN (>4×10{sup 18} cm{sup −3}) have been investigated with high resolution x-ray photoemission spectroscopy. The valence band photoemission spectra show that the surface Fermi level decreases by approximately 0.08 eV with (NH{sub 4}){sub 2}S{sub x} treatment, resulting in a decrease of the downward band bending and up to a 70% reduction in the surface electron sheet density.

  16. A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

    Energy Technology Data Exchange (ETDEWEB)

    González-Hernández, Rafael, E-mail: rhernandezj@uninorte.edu.co [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); González-García, Alvaro [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia); Barragán-Yani, Daniel [Fachgebiet Material modellierung, Institut für Materialwissenschaft, Technische Universität Darmstadt, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); López-Pérez, William [Grupo de Investigación en Física Aplicada, Departamento de Física, Universidad del Norte, Barranquilla (Colombia)

    2014-09-30

    Highlights: • A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaces was carried out. • Surface energies are too low for LDA, but lower still for GGA and MGGA functionals, except for PBEsol. • PBEsol exhibits good lattice parameters and surface energies. • Surface intra-gap states reduce the band gap of the nonpolar GaN surfaces. • Slight changes in the dispersion of surface states were observed for the LDA, GGA, and MGGA functionals. - Abstract: A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaces was carried out using density-functional theory (DFT) with different approximations for the exchange-correlation energy (LDA, PBE, PBEsol, RPBE, TPSS, revTPSS, and HSE). The obtained data show that the GaN(101{sup ¯}0) (m-plane) is more energetically stable than the GaN(112{sup ¯}0) (a-plane) surface. However, these surfaces have similar surface relaxation geometry, with a Ga-N surface bond-length contraction of around 6–7% and a Ga-N surface rotational angle in the range of 6–9°. Our results show that the use of different exchange-correlation functionals does not significantly change the surface energy and surface geometry. In addition, we found the presence of surface intra-gap states that reduce the band gap of the nonpolar GaN surface with respect to the bulk value, in agreement with recent photoelectron and surface optical spectroscopy experiments.

  17. Surface structures from low energy electron diffraction: Atoms, small molecules and an ordered ice film on metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Materer, N.F.

    1995-09-01

    We investigated the surface bonding of various adsorbates (0, S, C{sub 2}H{sub 3} and NO) along with the resulting relaxation of the Pt(111) surface using low energy electron diffiraction (LEED). LEED experiments have been performed on these ordered overlayers along with theoretical structural analysis using automated tensor LEED (ATLEED). The resulting surface structures of these ordered overlayers exhibit similar adsorbate-induced relaxations. In all cases the adsorbate occupies the fcc hollow site and induces an approximately 0.1 A buckling of the metal surface. The three metal atoms directly bonded to the adsorbate are ``pulled`` out of the surface and the metal atom that is not bound to the adsorbate is `pushed`` inward. In order to understand the reliability of such details, we have carried out a comprehensive study of various non-structural parameters used in a LEED computation. We also studied the adsorption of water on the Pt(lll) surface. We ordered an ultra thin ice film on this surface. The film`s surface is found to be the (0001) face of hexagonal ice. This surface is apparently terminated by a full-bilayer, in which the uppermost water molecules have large vibrational amplitudes even at temperatures as low as 90 K. We examined two other metal surfaces besides Pt(111): Ni(111) and Fe(lll). On Ni(111), we have studied the surface under a high coverage of NO. On both Ni(111) and Pt(111) NO molecules occupy the hollow sites and the N-0 bond distances are practically identical. The challenging sample preparation of an Fe(111) surface has been investigated and a successful procedure has been obtained. The small interlayer spacing found on Fe(111) required special treatment in the LEED calculations. A new ATLEED program has been developed to handle this surface.

  18. Fabrication of surface micro- and nanostructures for superhydrophobic surfaces in electric and electronic applications

    Science.gov (United States)

    Xiu, Yonghao

    In our study, the superhydrophobic surface based on biomimetic lotus leave is explored to maintain the desired properties for self-cleaning. Parameters in controlling bead-up and roll-off characteristics of water droplets were investigated on different model surfaces. The governing equations were proposed. Heuristic study is performed. First, the fundamental understanding of the effect of roughness on superhydrophobicity is performed. The effect of hierarchical roughness, i.e., two scale roughness effect on roughness is investigated using systems of (1) monodisperse colloidal silica sphere (submicron) arrays and Au nanoparticle on top and (2) Si micrometer pyramids and Si nanostructures on top from KOH etching and metal assisted etching of Si. The relation between the contact area fraction and water droplet contact angles are derived based on Wenzel and Cassie-Baxter equation for the systems and the two scale effect is explained regarding the synergistic combination of two scales. Previously the microscopic three-phase-contact line is thought to be the key factor in determining contact angles and hystereses. In our study, Laplace pressure was brought up and related to the three-phase-contact line and taken as a key figure of merit in determining superhydrophobicity. In addition, we are one of the first to study the effect of tapered structures (wall inclination). Combining with a second scale roughness on the tapered structures, stable Cassie state for both water and low surface energy oil may be achieved. This is of great significance for designing both superhydrophobicity and superoleophobicity. Regarding the origin of contact angle hysteresis, study of superhydrophobicity on micrometer Si pillars was performed. The relation between the interface work of function and contact angle hysteresis was proposed and derived mathematically based on the Young-Dupre equation. The three-phase-contact line was further related to a secondary scale roughness induced. Based on

  19. Multielectron bubbles in helium as a paradigm for studying electrons on surfaces with curvature

    Energy Technology Data Exchange (ETDEWEB)

    Tempere, J. [Lyman Laboratory of Physics, Harvard University, Cambridge MA 02138 (United States); TFVS, Universiteit Antwerpen, Groenenborgerlaan 171, B2020 Antwerpen (Belgium); Silvera, I.F. [Lyman Laboratory of Physics, Harvard University, Cambridge MA 02138 (United States); Devreese, J.T. [TFVS, Universiteit Antwerpen, Groenenborgerlaan 171, B2020 Antwerpen (Belgium)

    2007-05-31

    The study of two-dimensional electronic systems has revealed a host of new and startling phenomena, such as the quantum Hall effect. Although effort has gone into studying the effects of confinement in two-dimensional systems, the effects of surface curvature remain relatively unexplored. Nevertheless, curvature and surface topology are expected to have a profound influence: for example, on a sphere it is not possible to have a non-trivial current field that has no vortex structure in it. The spherical geometry also influences lattices in that topological lattice defects are always present. In this report, we present results and recent insights into the physics of electrons on spherical surfaces. In particular, we investigate the case of multielectron bubbles. Multielectron bubbles are (micron sized) cavities inside liquid helium, containing electrons that collect in a nanometer thin film on the surface of the bubble and form a spherical two-dimensional electronic system. Different phases are identified and investigated: the electron fluid, the Wigner lattice, and the pair-correlated 'superconducting' state. Uniaxial external magnetic fields (normal to the surface at the poles of the sphere, and tangential to the surface at the equator) influence the different phases and give rise to textures on the surface. In discussing the properties of the spherical electron system under various conditions, we identify the differences between flat surfaces and spherical surfaces. The theoretical framework presented here is focused on the case of electrons on the spherical surface of a bubble in helium. We discuss how the theory can straightforwardly be generalized to investigate the case of (finite thickness) metallic nanoshells. Nanoshells consist of a non-conducting nanograin covered by a few atomic layers of metal. The physiologically compatible size and unique optical properties of these objects have led to applications in diagnostics and directed therapeutics of

  20. Multielectron bubbles in helium as a paradigm for studying electrons on surfaces with curvature

    Science.gov (United States)

    Tempere, J.; Silvera, I. F.; Devreese, J. T.

    2007-05-01

    The study of two-dimensional electronic systems has revealed a host of new and startling phenomena, such as the quantum Hall effect. Although effort has gone into studying the effects of confinement in two-dimensional systems, the effects of surface curvature remain relatively unexplored. Nevertheless, curvature and surface topology are expected to have a profound influence: for example, on a sphere it is not possible to have a non-trivial current field that has no vortex structure in it. The spherical geometry also influences lattices in that topological lattice defects are always present. In this report, we present results and recent insights into the physics of electrons on spherical surfaces. In particular, we investigate the case of multielectron bubbles. Multielectron bubbles are (micron sized) cavities inside liquid helium, containing electrons that collect in a nanometer thin film on the surface of the bubble and form a spherical two-dimensional electronic system. Different phases are identified and investigated: the electron fluid, the Wigner lattice, and the pair-correlated "superconducting" state. Uniaxial external magnetic fields (normal to the surface at the poles of the sphere, and tangential to the surface at the equator) influence the different phases and give rise to textures on the surface. In discussing the properties of the spherical electron system under various conditions, we identify the differences between flat surfaces and spherical surfaces. The theoretical framework presented here is focused on the case of electrons on the spherical surface of a bubble in helium. We discuss how the theory can straightforwardly be generalized to investigate the case of (finite thickness) metallic nanoshells. Nanoshells consist of a non-conducting nanograin covered by a few atomic layers of metal. The physiologically compatible size and unique optical properties of these objects have led to applications in diagnostics and directed therapeutics of cancer and

  1. Excess electrons at anatase TiO2 surfaces and interfaces: insights from first principles simulations

    Science.gov (United States)

    Selçuk, Sencer; Selloni, Annabella

    2017-07-01

    TiO2 is an important technological material with widespread applications in photocatalysis, photovoltaics and self-cleaning surfaces. Excess electrons from intrinsic defects, dopants and photoexcitation play a key role in the properties of TiO2 that are relevant to its energy-related applications. The picture of excess and photoexcited electrons in TiO2 is based on the polaron model, where the electron forms a localized state that is stabilized by an accompanying lattice distortion. Here, we focus on excess and photoexcited electrons in anatase, the TiO2 polymorph most relevant to photocatalysis and solar energy conversion. For anatase, evidence of both small and large electron polarons has been reported in the literature. In addition, several studies have revealed a remarkable dependence of the photocatalytic activity of anatase on the crystal surface. After an overview of experimental studies, we briefly discuss recent progress in the theoretical description of polaronic states in TiO2, and finally present a more detailed account of our computational studies on the trapping and dynamics of excess electrons near the most common anatase surfaces and aqueous interfaces. The results of these studies provide a bridge between surface science experiments under vacuum conditions and observations of crystal-face-dependent photocatalysis on anatase, and support the idea that optimization of the ratio between different anatase facets can help enhance the photocatalytic activity of this material.

  2. Modulating semiconductor surface electronic properties by inorganic peptide-binders sequence design.

    Science.gov (United States)

    Matmor, Maayan; Ashkenasy, Nurit

    2012-12-19

    The use of proteins and peptides as part of biosensors and electronic devices has been the focus of intense research in recent years. However, despite the fact that the interface between the bioorganic molecules and the inorganic matter plays a significant role in determining the properties of such devices, information on the electronic properties of such interfaces is sparse. In this work, we demonstrate that the identity and position of single amino acid in short inorganic binding protein-segments can significantly modulate the electronic properties of semiconductor surfaces on which they are bound. Specifically, we show that the introduction of tyrosine or tryptophan, both possessing an aromatic side chain which higher occupied molecular orbitals are positioned in proximity to the edge of GaAs valence band, to the sequence of a peptide that binds to GaAs (100) results in changes of both the electron affinity and surface potential of the semiconductor. These effects were found to be more pronounced than the effects induced by the same amino acids once bound on the surface in a head-tail configuration. Furthermore, the relative magnitude of each effect was found to depend on the position of the modification in the sequence. This sequence dependent behavior is induced both indirectly by changes in the peptide surface coverage, and directly, probably, due to changes in the orientation and proximity of the tyrosine/tryptophan side group with respect to the surface due to the preferred conformation the peptide adopts on the surface. These studies reveal that despite the use of short protein oligomers and aiming at a non-natural-electronic task, the well-known relations between the proteins' structure and function is preserved. Combining the ability to tune the electronic properties at the interface with the ability to direct the growth of inorganic materials makes peptides promising building blocks for the construction of novel hybrid electronic devices and biosensors.

  3. Copper plasmonics and catalysis: role of electron-phonon interactions in dephasing localized surface plasmons.

    Science.gov (United States)

    Sun, Qi-C; Ding, Yuchen; Goodman, Samuel M; Funke, Hans H; Nagpal, Prashant

    2014-11-07

    Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain boundary scattering on the decay of localized surface plasmon waves. Using our quantitative analysis and different temperature dependent measurements, we show that electron-phonon interactions dominate over other scattering mechanisms in dephasing plasmon waves. While interband transitions in copper metal contributes substantially to plasmon losses, tuning surface plasmon modes to infrared frequencies leads to a five-fold enhancement in the quality factor. These findings demonstrate that conformal ALD coatings can improve the chemical stability for copper nanoparticles, even at high temperatures (>300 °C) in ambient atmosphere, and nanoscaled copper is a good alternative material for many potential applications in nanophotonics, plasmonics, catalysis and nanoscale electronics.

  4. Tuning the electronic properties at the surface of BaBiO3 thin films

    Science.gov (United States)

    Ferreyra, C.; Guller, F.; Marchini, F.; Lüders, U.; Albornoz, C.; Leyva, A. G.; Williams, F. J.; Llois, A. M.; Vildosola, V.; Rubi, D.

    2016-06-01

    The presence of 2D electron gases at surfaces or interfaces in oxide thin films remains a hot topic in condensed matter physics. In particular, BaBiO3 appears as a very interesting system as it was theoretically proposed that its (001) surface should become metallic if a Bi-termination is achieved (Vildosola et al., PRL 110, 206805 (2013)). Here we report on the preparation by pulsed laser deposition and characterization of BaBiO3 thin films on silicon. We show that the texture of the films can be tuned by controlling the growth conditions, being possible to stabilize strongly (100)-textured films. We find significant differences on the spectroscopic and transport properties between (100)-textured and non-textured films. We rationalize these experimental results by performing first principles calculations, which indicate the existence of electron doping at the (100) surface. This stabilizes Bi ions in a 3+ state, shortens Bi-O bonds and reduces the electronic band gap, increasing the surface conductivity. Our results emphasize the importance of surface effects on the electronic properties of perovskites, and provide strategies to design novel oxide heterostructures with potential interface-related 2D electron gases.

  5. Tuning the electronic properties at the surface of BaBiO3 thin films

    Directory of Open Access Journals (Sweden)

    C. Ferreyra

    2016-06-01

    Full Text Available The presence of 2D electron gases at surfaces or interfaces in oxide thin films remains a hot topic in condensed matter physics. In particular, BaBiO3 appears as a very interesting system as it was theoretically proposed that its (001 surface should become metallic if a Bi-termination is achieved (Vildosola et al., PRL 110, 206805 (2013. Here we report on the preparation by pulsed laser deposition and characterization of BaBiO3 thin films on silicon. We show that the texture of the films can be tuned by controlling the growth conditions, being possible to stabilize strongly (100-textured films. We find significant differences on the spectroscopic and transport properties between (100-textured and non-textured films. We rationalize these experimental results by performing first principles calculations, which indicate the existence of electron doping at the (100 surface. This stabilizes Bi ions in a 3+ state, shortens Bi-O bonds and reduces the electronic band gap, increasing the surface conductivity. Our results emphasize the importance of surface effects on the electronic properties of perovskites, and provide strategies to design novel oxide heterostructures with potential interface-related 2D electron gases.

  6. SiGe Based Low Temperature Electronics for Lunar Surface Applications

    Science.gov (United States)

    Mojarradi, Mohammad M.; Kolawa, Elizabeth; Blalock, Benjamin; Cressler, John

    2012-01-01

    The temperature at the permanently shadowed regions of the moon's surface is approximately -240 C. Other areas of the lunar surface experience temperatures that vary between 120 C and -180 C during the day and night respectively. To protect against the large temperature variations of the moon surface, traditional electronics used in lunar robotics systems are placed inside a thermally controlled housing which is bulky, consumes power and adds complexity to the integration and test. SiGe Based electronics have the capability to operate over wide temperature range like that of the lunar surface. Deploying low temperature SiGe electronics in a lander platform can minimize the need for the central thermal protection system and enable the development of a new generation of landers and mobility platforms with highly efficient distributed architecture. For the past five years a team consisting of NASA, university and industry researchers has been examining the low temperature and wide temperature characteristic of SiGe based transistors for developing electronics for wide temperature needs of NASA environments such as the Moon, Titan, Mars and Europa. This presentation reports on the status of the development of wide temperature SiGe based electronics for the landers and lunar surface mobility systems.

  7. Tuning the electronic properties at the surface of BaBiO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Ferreyra, C. [GIyA y INN, CNEA, Av.Gral Paz 1499, (1650), San Martín, Buenos Aires (Argentina); Departamento de Física, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires (Argentina); Guller, F.; Llois, A. M.; Vildosola, V. [GIyA y INN, CNEA, Av.Gral Paz 1499, (1650), San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Argentina); Marchini, F.; Williams, F. J. [Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Argentina); Departamento de Química Inorgánica, Analítica y Química-Física, INQUIMAE-CONICET, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, Buenos Aires (Argentina); Lüders, U. [CRISMAT, CNRS UMR 6508, ENSICAEN, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4 (France); Albornoz, C. [GIyA y INN, CNEA, Av.Gral Paz 1499, (1650), San Martín, Buenos Aires (Argentina); Leyva, A. G. [GIyA y INN, CNEA, Av.Gral Paz 1499, (1650), San Martín, Buenos Aires (Argentina); Escuela de Ciencia y Tecnología, UNSAM, Campus Miguelete, (1650), San Martín, Buenos Aires (Argentina); and others

    2016-06-15

    The presence of 2D electron gases at surfaces or interfaces in oxide thin films remains a hot topic in condensed matter physics. In particular, BaBiO{sub 3} appears as a very interesting system as it was theoretically proposed that its (001) surface should become metallic if a Bi-termination is achieved (Vildosola et al., PRL 110, 206805 (2013)). Here we report on the preparation by pulsed laser deposition and characterization of BaBiO{sub 3} thin films on silicon. We show that the texture of the films can be tuned by controlling the growth conditions, being possible to stabilize strongly (100)-textured films. We find significant differences on the spectroscopic and transport properties between (100)-textured and non-textured films. We rationalize these experimental results by performing first principles calculations, which indicate the existence of electron doping at the (100) surface. This stabilizes Bi ions in a 3+ state, shortens Bi-O bonds and reduces the electronic band gap, increasing the surface conductivity. Our results emphasize the importance of surface effects on the electronic properties of perovskites, and provide strategies to design novel oxide heterostructures with potential interface-related 2D electron gases.

  8. Surface charging of phosphors and its effects on cathodoluminescence at low electron energies

    Energy Technology Data Exchange (ETDEWEB)

    Seager, C.H.; Warren, W.L.; Tallant, D.R.

    1997-05-01

    Measurements of the threshold for secondary electron emission and shifts of the carbon Auger line position have been used to deduce the surface potential of several common phosphors during irradiation by electrons in the 0.5--5.0 keV range. All of the insulating phosphors display similar behavior: the surface potential is within {+-}1 V of zero at low electron energies. However, above 2--3 kV it becomes increasingly negative, reaching hundreds of volts within 1 keV of the turn-on energy. The electron energy at which this charging begins decreases dramatically after Coulomb aging at 17 {micro}A/cm{sup 2} for 30--60 min. Measurements using coincident electron beams at low and high electron energies to control the surface potential were made to investigate the dependence of the cathodoluminescence (CL) process on charging. Initially, the CL from the two beams is identical to the sum of the separate beam responses, but after Coulomb aging large deviations from this additivity are observed. These results indicate that charging has important, detrimental effects on CL efficiency after prolonged e-beam irradiation. Measurements of the electron energy dependence of the CL efficiency before and after Coulomb aging will also be presented, and the implications of these data on the physics of the low-voltage CL process will be discussed.

  9. Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces

    Science.gov (United States)

    Kaiser, W. J.; Bell, L. D.; Hecht, M. H.; Grunthaner, F. J.

    1988-01-01

    Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si-SiO2 interface. STM images directly reveal the topographic structure of the Si-SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.

  10. Hot electron mediated desorption rates calculated from excited state potential energy surfaces

    CERN Document Server

    Olsen, Thomas; Schiøtz, Jakob

    2008-01-01

    We present a model for Desorption Induce by (Multiple) Electronic Transitions (DIET/DIMET) based on potential energy surfaces calculated with the Delta Self-Consistent Field extension of Density Functional Theory. We calculate potential energy surfaces of CO and NO molecules adsorbed on various transition metal surfaces, and show that classical nuclear dynamics does not suffice for propagation in the excited state. We present a simple Hamiltonian describing the system, with parameters obtained from the excited state potential energy surface, and show that this model can describe desorption dynamics in both the DIET and DIMET regime, and reproduce the power law behavior observed experimentally. We observe that the internal stretch degree of freedom in the molecules is crucial for the energy transfer between the hot electrons and the molecule when the coupling to the surface is strong.

  11. Investigation of the electron emission properties of silver: From exposed to ambient atmosphere Ag surface to ion-cleaned Ag surface

    Energy Technology Data Exchange (ETDEWEB)

    Gineste, T., E-mail: Thomas.Gineste@onera.fr [ONERA The French Aerospace Lab, 31055 Toulouse (France); Belhaj, M. [ONERA The French Aerospace Lab, 31055 Toulouse (France); Teyssedre, G. [LAPLACE - Laboratoire Plasma et Conversion d’Energie -UMR 5213, Université Paul Sabatier - 118, route de Narbonne, 31062 Toulouse Cedex (France); Puech, J. [CNES, 18 Avenue Edouard Belin 31055 Toulouse Cédex 9 (France)

    2015-12-30

    Highlights: • We investigated the electron emission yield of an air exposed Ag to a cleaned Ag. • Air exposed Ag sample was cleaned by ion Ar etching. • Surface composition was determined by AES. • Electron emission yield was related to surface composition evolution. • Natural contamination hugely influence electron properties of Ag sample. - Abstract: Electron emission properties of materials are highly dependent to the surface and the first nanometres subsurface. Technical materials, i.e. used within applications are ordinarily exposed to atmosphere, which interacts with the surface. The contamination layer building up at the surface of materials and/or oxidation layer affects dramatically the electron emission proprieties. In this paper, starting from 99.99% pure silver sample, exposed 4 years to ambient atmosphere, we monitored the variations of the electron emission properties and the surface composition during step by step ion etching procedure.

  12. 4D scanning ultrafast electron microscopy: visualization of materials surface dynamics.

    Science.gov (United States)

    Mohammed, Omar F; Yang, Ding-Shyue; Pal, Samir Kumar; Zewail, Ahmed H

    2011-05-25

    The continuous electron beam of conventional scanning electron microscopes (SEM) limits the temporal resolution required for the study of ultrafast dynamics of materials surfaces. Here, we report the development of scanning ultrafast electron microscopy (S-UEM) as a time-resolved method with resolutions in both space and time. The approach is demonstrated in the investigation of the dynamics of semiconducting and metallic materials visualized using secondary-electron images and backscattering electron diffraction patterns. For probing, the electron packet was photogenerated from the sharp field-emitter tip of the microscope with a very low number of electrons in order to suppress space-charge repulsion between electrons and reach the ultrashort temporal resolution, an improvement of orders of magnitude when compared to the traditional beam-blanking method. Moreover, the spatial resolution of SEM is maintained, thus enabling spatiotemporal visualization of surface dynamics following the initiation of change by femtosecond heating or excitation. We discuss capabilities and potential applications of S-UEM in materials and biological science.

  13. Van der Waals Layered Materials: Surface Morphology, Interlayer Interaction, and Electronic Structure

    Science.gov (United States)

    Yeh, Po-Chun

    The search for new ultrathin materials as the "new silicon" has begun. In this dissertation, I examine (1) the surface structure, including the growth, the crystal quality, and thin film surface corrugation of a monolayer sample and a few layers of MoS2 and WSe2, and (2) their electronic structure. The characteristics of these electronic systems depend intimately on the morphology of the surfaces they inhabit, and their interactions with the substrate or within layers. These physical properties will be addressed in each chapter. This thesis has dedicated to the characterization of mono- and a few layers of MoS2 and WSe2 that uses surface-sensitive probes such as low-energy electron microscopy and diffraction (LEEM and LEED). Prior to our studies, the characterization of monolayer MoS2 and WSe2 has been generally limited to optical and transport probes. Furthermore, the heavy use of thick silicon oxide layer as the supporting substrate has been important in order to allow optical microscopic characterization of the 2D material. Hence, to the best of our knowledge, this has prohibited studies of this material on other surfaces, and it has precluded the discovery of potentially rich interface interactions that may exist between MoS 2 and its supporting substrate. Thus, in our study, we use a so-called SPELEEM system (Spectroscopic Photo-Emission and Low Energy Electron Microscopy) to address these imaging modalities: (1) real-space microscopy, which would allow locating of monolayer MoS2 samples, (2) spatially-resolved low-energy diffraction which would allow confirmation of the crystalline quality and domain orientation of MoS2 samples, and, (3) spatially-resolved spectroscopy, which would allow electronic structure mapping of MoS2 samples. Moreover, we have developed a preparation procedure for samples that yield, a surface-probe ready, ultra-clean, and can be transferred on an arbitrary substrate. To fully understand the physics in MoS2 such as direct

  14. Nanopatterning of mobile lipid monolayers on electron-beam-sculpted Teflon AF surfaces.

    Science.gov (United States)

    Shaali, Mehrnaz; Lara-Avila, Samuel; Dommersnes, Paul; Ainla, Alar; Kubatkin, Sergey; Jesorka, Aldo

    2015-02-24

    Direct electron-beam lithography is used to fabricate nanostructured Teflon AF surfaces, which are utilized to pattern surface-supported monolayer phospholipid films with 50 nm lateral feature size. In comparison with unexposed Teflon AF coatings, e-beam-irradiated areas show reduced surface tension and surface potential. For phospholipid monolayer spreading experiments, these areas can be designed to function as barriers that enclose unexposed areas of nanometer dimensions and confine the lipid film within. We show that the effectiveness of the barrier is defined by pattern geometry and radiation dose. This surface preparation technique represents an efficient, yet simple, nanopatterning strategy supporting studies of lipid monolayer behavior in ultraconfined spaces. The generated structures are useful for imaging studies of biomimetic membranes and other specialized surface applications requiring spatially controlled formation of self-assembled, molecularly thin films on optically transparent patterned polymer surfaces with very low autofluorescence.

  15. New aspects of electronic excitations at the bismuth surface: Topology, thermalization and coupling to coherent phonons

    Energy Technology Data Exchange (ETDEWEB)

    Perfetti, L., E-mail: luca.perfetti@polytechnique.edu [Laboratoire des Solides Irradiés, Ecole Polytechnique – CEA/DSM – CNRS UMR 7642, 91128 Palaiseau (France); Faure, J. [Laboratoire d’Optique Appliquée, Ecole Polytechnique – ENSTA – CNRS UMR 7639, 91761 Palaiseau (France); Papalazarou, E.; Mauchain, J.; Marsi, M.; Goerbig, M.O. [Laboratoire de Physique des Solides, CNRS UMR 8502, Université Paris-Sud, F-91405 Orsay (France); Taleb-Ibrahimi, A.; Ohtsubo, Y. [Synchrotron SOLEIL, Saint-Aubin-BP 48, F-91192 Gif sur Yvette (France)

    2015-05-15

    We review measurements of angle and time resolved photoelectron spectroscopy on the surface states of the Bi(1 1 1) surface. The work covers several aspects of these surface states, discussing the topological properties, the strong anisotropy of the spin–orbit splitting and the dynamical relaxation of photoexcited electrons. Since time resolved experiments disentagle interaction processes in real time, the reported data offer a novel perspective on the motion of charge carriers in surface states and will serve as an unuseful reference for other systems with strong spin–orbit coupling.

  16. Equilibrium Geometries, Reaction Pathways, and Electronic Structures of Ethanol Adsorbed on the Si (111) Surface

    CERN Document Server

    Gavrilenko, A V; Gavrilenko, V I

    2008-01-01

    Equilibrium atomic configurations and electron energy structure of ethanol adsorbed on the Si (111) surface are studied by the first-principles density functional theory. Geometry optimization is performed by the total energy minimization method. Several equilibrium atomic configurations of ethanol, both undissociated and dissociated, on the Si (111) surface are found. Reaction pathways and predicted transition states are discussed in comparison with available experimental data in terms of the feasibility of the reactions occurring. Analysis of atom and orbital resolved projected density of states indicate substantial modifications of the Si surface valence and conduction bands due to the adsorption of ethanol affecting the electrical properties of the surface.

  17. Geometric and electronic structure of dysprosium thin films on tungsten surfaces Structural and magnetic properties

    CERN Document Server

    Moslemzadeh, N

    2001-01-01

    The rare earth thin films are frequently the focus of investigators due to their unusual structural and magnetic properties. Despite the potential interest of Dy/W systems to the surface/rare earth community, they have been little studied. This study is the first try of growing Dy on W(100) and W(112) and W(110) in which almost a complete set of information about film morphology and electronic structure of the surface and interface have been achieved. A set of different experiments have been done for this purpose including LEED, XPS, UPS (with synchrotron radiation) and STM. The growth modes of Dy on different W substrates (W(100), W(112) and W(110)) at RT and at elevated temperatures have been determined by XPS of Dy 3d sub 3 sub / sub 2 and W 4f intensities. Crystallographic ordering and the epitaxial relationship between adsorbate Dy and different W substrates have been studied with LEED and the effect of annealing temperature on the resultant superstructures was investigated. As a complementary study to t...

  18. Electron scattering at surfaces and grain boundaries in thin Au films

    Energy Technology Data Exchange (ETDEWEB)

    Henriquez, Ricardo [Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Casilla 110-V, Valparaíso (Chile); Flores, Marcos; Moraga, Luis [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Kremer, German [Bachillerato, Universidad de Chile, Las Palmeras 3425, Santiago 7800024 (Chile); González-Fuentes, Claudio [Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Casilla 110-V, Valparaíso (Chile); Munoz, Raul C., E-mail: ramunoz@ing.uchile.cl [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile)

    2013-05-15

    The electron scattering at surfaces and grain boundaries is investigated using polycrystalline Au films deposited onto mica substrates. We vary the three length scales associated with: (i) electron scattering in the bulk, that at temperature T is characterized by the electronic mean free path in the bulk ℓ{sub 0}(T); (ii) electron-surface scattering, that is characterized by the film thickness t; (iii) electron-grain boundary scattering, that is characterized by the mean grain diameter D. We varied independently the film thickness from approximately 50 nm to about 100 nm, and the typical grain size making up the samples from 12 nm to 160 nm. We also varied the scale of length associated with electron scattering in the bulk by measuring the resistivity of each specimen at temperatures T, 4 K < T < 300 K. Cooling the samples to 4 K increases ℓ{sub 0}(T) by approximately 2 orders of magnitude. Detailed measurements of the grain size distribution as well as surface roughness of each sample were performed with a Scanning Tunnelling Microscope (STM). We compare, for the first time, theoretical predictions with resistivity data employing the two theories available that incorporate the effect of both electron-surface as well as electron-grain boundary scattering acting simultaneously: the theory of A.F. Mayadas and M. Shatzkes, Phys. Rev. 1 1382 (1970) (MS), and that of G. Palasantzas, Phys. Rev. B 58 9685 (1998). We eliminate adjustable parameters from the resistivity data analysis, by using as input the grain size distribution as well as the surface roughness measured with the STM on each sample. The outcome is that both theories provide a fair representation of both the temperature as well as the thickness dependence of the resistivity data, but yet there are marked differences between the resistivity predicted by these theories. In the case of the MS theory, when the average grain diameter D is significantly smaller than ℓ{sub 0}(300) = 37 nm, the electron mean

  19. Surface-conduction electron-emitter characteristics and fabrication based on vertically aligned carbon nanotube arrays

    Science.gov (United States)

    Shih, Yi-Ting; Li, Kuan-Wei; Honda, Shin-ichi; Lin, Pao-Hung; Huang, Ying-Sheng; Lee, Kuei-Yi

    2017-06-01

    The carbon nanotube (CNT) has replaced palladium oxide (PdO) as the electrode material for surface-conduction electron-emitter (SCE) applications. Vertically aligned CNT arrays with a delta-star arrangement were patterned and synthesized onto a quartz substrate using photolithography and thermal chemical vapor deposition. Delta-star shaped VACNT arrays with 20° tips are used as cathodes that easily emit electrons because of their high electrical field gradient. In order to improve the field emission and secondary electrons (SEs) in SCE applications, magnesium oxide (MgO) nanostructures were coated onto the VACNT arrays to promote the surface-conduction electron-emitter display (SED) efficiency (η). According to the definition of η in SCE applications, in this study, the η was stably maintained in the 75-85% range. The proposed design provides a facile new method for developing SED applications.

  20. Controlling multipolar surface plasmon excitation through the azimuthal phase structure of electron vortex beams

    Science.gov (United States)

    Ugarte, Daniel; Ducati, Caterina

    2016-05-01

    We have theoretically studied how the azimuthal phase structure of an electron vortex beam excites surface plasmons on metal particles of different geometries as observed in electron energy loss spectroscopy (EELS). We have developed a semiclassical approximation combining a ring-shaped beam and the dielectric formalism. Our results indicate that for the case of total orbital angular momentum transfer, we can manipulate surface plasmon multipole excitation and even attain an enhancement factor of several orders of magnitude. Since electron vortex beams interact with particles mostly through effects due to azimuthal symmetry, i.e., in the plane perpendicular to the electron beam, anisotropy information (longitudinal and transversal) of the sample may be derived in EELS studies by comparing nonvortex and vortex beam measurements.

  1. Thermal effects in equilibrium surface segregation in a copper/10-atomic-percent-aluminum alloy using Auger electron spectroscopy

    Science.gov (United States)

    Ferrante, J.

    1972-01-01

    Equilibrium surface segregation of aluminum in a copper-10-atomic-percent-aluminum single crystal alloy oriented in the /111/ direction was demonstrated by using Auger electron spectroscopy. This crystal was in the solid solution range of composition. Equilibrium surface segregation was verified by observing that the aluminum surface concentration varied reversibly with temperature in the range 550 to 850 K. These results were curve fitted to an expression for equilibrium grain boundary segregation and gave a retrieval energy of 5780 J/mole (1380 cal/mole) and a maximum frozen-in surface coverage three times the bulk layer concentration. Analyses concerning the relative merits of sputtering calibration and the effects of evaporation are also included.

  2. Core-shell nanowire based electrical surface fastener used for room-temperature electronic packaging bonding

    Science.gov (United States)

    Wang, Peng; Ju, Yang; Hosoi, Atsushi

    2014-03-01

    With the ongoing miniaturization in electronic packaging, the traditional solders suffer from severe performance degradation. In addition, the high temperature required in the traditional solder reflow process may damage electronic elements. Therefore, there is an increasing urgent need for a new kind of nontoxic solder that can afford good mechanical stress and electrical contact at low temperature. This paper presents a method of fabricating nanowire surface fastener for the application of microelectronic packaging bonding at room temperature. This surface fastener consists of copper core and polystyrene shell nanowire arrays. It showed an adhesive strength of ˜24 N/cm2 and an electrical resistance of ˜0.41 × 10-2 Ω·cm2. This kind of nanowire surface fastener may enable the exploration of wide range applications, involving assembly of components in the electronic packaging.

  3. Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

    Science.gov (United States)

    Santander-Syro, A. F.; Fortuna, F.; Bareille, C.; Rödel, T. C.; Landolt, G.; Plumb, N. C.; Dil, J. H.; Radović, M.

    2014-12-01

    Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides exhibit a range of properties, including tunable insulator-superconductor-metal transitions, large magnetoresistance, coexisting ferromagnetism and superconductivity, and a spin splitting of a few meV (refs , ). Strontium titanate (SrTiO3), the cornerstone of such oxide-based electronics, is a transparent, non-magnetic, wide-bandgap insulator in the bulk, and has recently been found to host a surface 2DEG (refs , , , ). The most strongly confined carriers within this 2DEG comprise two subbands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces. Using spin- and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these subbands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated. Moreover, in contrast to a simple Rashba system, the spin-polarized subbands are non-degenerate at the Brillouin zone centre. This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.

  4. Electronic circuits and systems: A compilation. [including integrated circuits, logic circuits, varactor diode circuits, low pass filters, and optical equipment circuits

    Science.gov (United States)

    1975-01-01

    Technological information is presented electronic circuits and systems which have potential utility outside the aerospace community. Topics discussed include circuit components such as filters, converters, and integrators, circuits designed for use with specific equipment or systems, and circuits designed primarily for use with optical equipment or displays.

  5. Electron microscopy observations of surface morphologies and particle arrangement behaviors of magnetic fluids

    Institute of Scientific and Technical Information of China (English)

    沈辉; 徐雪青; 王伟

    2003-01-01

    The surface morphology of quasi-periodic stripe-shaped patterns of magnetite fluids was observed in applied perpendicular magnetic fields by means of scanning electron microscopy. The nanoparticles of the magnetite fluids are arranged in oriental quasilinear chains in applied perpendicular magnetic fields as observed using transmission electron microscopy. This arrangement results from particle-particle interactions and particle-carrier liquids interactions, which are eventually controlled by the magnetic fields distribution.

  6. Sub-molecular electronic structure of self-assembled metal-organic nano-chains on a noble metal surface

    Science.gov (United States)

    Schiffrin, Agustin; Capsoni, Martina; Shaw, Adam; Burke, Sarah

    2014-03-01

    Complexes composed of organic ligands coordinated with transition metal atoms exhibit broad absorption bands from the ultraviolet to the near-infrared. These are the result of the intrinsic molecular electronic properties, which include intra-ligand excitations and metal-to-ligand charge transfer. When adsorbed on a surface, these compounds are relevant for photovoltaic applications. In order to ensure a hierarchical transfer of function from the nano- to the macro-scale, electronic characterization at the single molecule level is essential. We present a low-temperature scanning tunneling spectroscopy study on the local electronic structure of one-dimensional self-assembled metal-organic nanostructures formed on a noble metal surface. The nano-chains consist of terpyridine-based ligands coordinated with iron (Fe) adatoms. We map the local density of electronic states of the system with sub-molecular spatial resolution. Energy-broadened highest-occupied molecular orbitals are dominated by metal states, whereas sharp resonances above Fermi are mainly related to the organic moiety. Coordination between the ligand and Fe induces energy shifts and a break of spatial symmetry of the unoccupied states, pointing to an electron transfer from the metal atom to the terpyridine groups.

  7. Hot electron dynamics at semiconductor surfaces: Implications for quantum dot photovoltaics

    Science.gov (United States)

    Tisdale, William A., III

    Finding a viable supply of clean, renewable energy is one of the most daunting challenges facing the world today. Solar cells have had limited impact in meeting this challenge because of their high cost and low power conversion efficiencies. Semiconductor nanocrystals, or quantum dots, are promising materials for use in novel solar cells because they can be processed with potentially inexpensive solution-based techniques and because they are predicted to have novel optoelectronic properties that could enable the realization of ultra-efficient solar power converters. However, there is a lack of fundamental understanding regarding the behavior of highly-excited, or "hot," charge carriers near quantum-dot and semiconductor interfaces, which is of paramount importance to the rational design of high-efficiency devices. The elucidation of these ultrafast hot electron dynamics is the central aim of this Dissertation. I present a theoretical framework for treating the electronic interactions between quantum dots and bulk semiconductor surfaces and propose a novel experimental technique, time-resolved surface second harmonic generation (TR-SHG), for probing these interactions. I then describe a series of experimental investigations into hot electron dynamics in specific quantum-dot/semiconductor systems. A two-photon photoelectron spectroscopy (2PPE) study of the technologically-relevant ZnO(1010) surface reveals ultrafast (sub-30fs) cooling of hot electrons in the bulk conduction band, which is due to strong electron-phonon coupling in this highly polar material. The presence of a continuum of defect states near the conduction band edge results in Fermi-level pinning and upward (n-type) band-bending at the (1010) surface and provides an alternate route for electronic relaxation. In monolayer films of colloidal PbSe quantum dots, chemical treatment with either hydrazine or 1,2-ethanedithiol results in strong and tunable electronic coupling between neighboring quantum dots

  8. Electron Emission from Cross-Sectional Surface of Porous Si on Glass Substrate

    Science.gov (United States)

    Katsuya Higa,

    2010-02-01

    The measurement of electron emission from the cross-sectional surface of porous Si layer on a glass substrate is demonstrated. The porous Si is formed by anodization, and subsequently bonded on a glass substrate with an Al electrode by anodic bonding. The electron emission device structure is composed of a Au electrode, a porous Si layer, and a glass substrate with an Al electrode. This structure is cut into two pieces during the formation of the cross-sectional surface of porous Si. The measurement of electron emission is carried out using a diode configuration in a vacuum chamber. A collector is placed close to the cross-sectional surface of porous Si. The negative voltages are applied at the Au electrode and electron emission from the cross-sectional surface of porous Si layer occurs. The characteristics of emission current are measured using the variation of applied negative voltage, the stability of electron emission, and the change in location of the Au electrode at the edge of the cross section of porous Si layer.

  9. Electron emission induced by resonant coherent interaction in ion-surface scattering at grazing incidence

    Energy Technology Data Exchange (ETDEWEB)

    Garcia de Abajo, F.J. (Departamento de Ciencias de la Computacion e Inteligencia Artificial, Facultad de Informatica, Universidad del Pais Vasco, Apartado 649, 20080 San Sebastian (Spain)); Ponce, V.H.; Echenique, P.M. (Departamento de Fisica de Materiales, Facultad de Quimica, Universidad del Pais Vasco, Apartado 1072, 20080 San Sebastian (Spain))

    1994-01-15

    The resonant coherent interaction of an ion with an oriented crystal surface, under grazing-incidence conditions with respect to a special direction of the crystal, gives rise to electron loss to the continuum from electronic bound states of the ion. The calculations presented below predict large probabilities for electron emission due to this mechanism. The electrons are emitted with well defined energies, expressed in terms of the condition of resonance. Furthermore, the emission takes place around certain preferential directions, which are determined by both the latter condition and the symmetry of the surface lattice. Our calculations for MeV He[sup +] ions scattered at a W(001) surface along the [l angle]100[r angle] direction with glancing angle of 0--2 mrad indicate a yield of emission close to 1. Using heavier projectiles, one obtains smaller yields, but still large enough to be measurable in some cases (e.g., [approx]0.9 for 53 MeV B[sup 4+] and an angle of incidence of 1 mrad). Besides, the initial bound state is energy shifted due to the interaction with both the crystal potential and the velocity-dependent image potential. This results in a slight shift of the peaks of emission, which suggests a possible spectroscopy for analyzing the dynamical interaction of electronic bound states with solid surfaces.

  10. Ab initio tensorial electronic friction for molecules on metal surfaces: Nonadiabatic vibrational relaxation

    Science.gov (United States)

    Maurer, Reinhard J.; Askerka, Mikhail; Batista, Victor S.; Tully, John C.

    2016-09-01

    Molecular adsorbates on metal surfaces exchange energy with substrate phonons and low-lying electron-hole pair excitations. In the limit of weak coupling, electron-hole pair excitations can be seen as exerting frictional forces on adsorbates that enhance energy transfer and facilitate vibrational relaxation or hot-electron-mediated chemistry. We have recently reported on the relevance of tensorial properties of electronic friction [M. Askerka et al., Phys. Rev. Lett. 116, 217601 (2016), 10.1103/PhysRevLett.116.217601] in dynamics at surfaces. Here we present the underlying implementation of tensorial electronic friction based on Kohn-Sham density functional theory for condensed phase and cluster systems. Using local atomic-orbital basis sets, we calculate nonadiabatic coupling matrix elements and evaluate the full electronic friction tensor in the Markov limit. Our approach is numerically stable and robust, as shown by a detailed convergence analysis. We furthermore benchmark the accuracy of our approach by calculation of vibrational relaxation rates and lifetimes for a number of diatomic molecules at metal surfaces. We find friction-induced mode-coupling between neighboring CO adsorbates on Cu(100) in a c (2 ×2 ) overlayer to be important for understanding experimental findings.

  11. The very surface states on GaAs(001) surface by means of electronic and optical techniques

    Science.gov (United States)

    Placidi, Ernesto

    2004-03-01

    Until now, Reflectance-Anisotropy Spectroscopy (RAS) in the visible has been the most used technique to quantify the anisotropy of these surfaces [1]. Low-energy electrons are believed to perturb more than photons and have not been employed to this purpose, despite their shorter penetration depth. In our presentation we show experimental results of High-Resolution Electron-Energy-Loss Spectroscopy (HREELS) applied to investigate the anisotropy of the GaAs(001)-c(4x4) and beta2(2x4) surfaces. We demonstrate the higher surface sensitivity of HREELS compared to RAS. Measurements are performed on high-quality samples grown in situ by Molecular Beam Epitaxy (MBE). The loss spectra taken in the two orthogonal surface directions have different intensities, particularly close to the fundamental gap, where surface like resonances, involving dimers, are observed. We discuss our HREELS and RAS data to identify the source of the anisotropy close to the critical point transitions where surface and bulk like excitations coexist. Our data are in very good agreement with DFT-LDA calculations for loss energies up to 3.5 eV [2]. The exposure of the reconstructed surfaces to molecular oxygen affects strongly the spectral features. [1] D.E.Aspnes, J.P.Harbison, A.A.Studna, L.T.Florez, Phys. Rev. Lett. 59 (1987) 1687; I.Kamiya, D.E.Aspnes, L.T.Florez, and J.T.Harbison, Phys. Rev. B 46 (1992) 15894. [2] A.Balzarotti, F.Arciprete, M.Fanfoni, F.Patella, E. Placidi, G.Onida, R.Del Sole, Surf. Sci. Lett. 524, L71 (2003); A.Balzarotti, E.Placidi, F.Arciprete, M.Fanfoni, F.Patella, Physical Review B, 67 115332 (2003); F.Arciprete, C. Goletti, E. Placidi, M.Fanfoni, F.Patella, P. Chiaradia, C. Hogan and A. Balzarotti, Phys. Rev. B 68 125328 (2003).

  12. Different quantization mechanisms in single-electron pumps driven by surface acoustic waves

    DEFF Research Database (Denmark)

    Utko, P.; Gloos, K.; Hansen, Jørn Bindslev

    2006-01-01

    We have studied the acoustoelectric current in single-electron pumps driven by surface acoustic waves. We have found that in certain parameter ranges two different sets of quantized steps dominate the acoustoelectric current versus gate-voltage characteristics. In some cases, both types of quanti......We have studied the acoustoelectric current in single-electron pumps driven by surface acoustic waves. We have found that in certain parameter ranges two different sets of quantized steps dominate the acoustoelectric current versus gate-voltage characteristics. In some cases, both types...

  13. Direct observation of spin-resolved full and empty electron states in ferromagnetic surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Berti, G., E-mail: giulia.berti@polimi.it; Calloni, A.; Brambilla, A.; Bussetti, G.; Duò, L.; Ciccacci, F. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133, Milano (Italy)

    2014-07-15

    We present a versatile apparatus for the study of ferromagnetic surfaces, which combines spin-polarized photoemission and inverse photoemission spectroscopies. Samples can be grown by molecular beam epitaxy and analyzed in situ. Spin-resolved photoemission spectroscopy analysis is done with a hemispherical electron analyzer coupled to a 25 kV-Mott detector. Inverse photoemission spectroscopy experiments are performed with GaAs crystals as spin-polarized electron sources and a UV bandpass photon detector. As an example, measurements on the oxygen passivated Fe(100)-p(1×1)O surface are presented.

  14. Electron beam surface hardening of 42CrMo4 steel

    Energy Technology Data Exchange (ETDEWEB)

    Jokinen, T.; Meuronen, I. [Valmet Aviation Industries, Linnavuori (Finland). Engine Maintenance

    1997-12-31

    A study is reported in this paper which aims to find the proper parameters of an electron beam machine for using electron beam (EB) hardening on 42CrMo4 steel. Extended service life for engineering components depends on hard, wear resistant surfaces combined with tough base materials. EB hardening is particularly suitable to local treatment of complex components. Although surface hardening of 42CrMo4 steel was successful, careful optimization of process parameters and the hardened layer are required. (UK).

  15. 30 CFR 785.19 - Surface coal mining and reclamation operations on areas or adjacent to areas including alluvial...

    Science.gov (United States)

    2010-07-01

    ..., and evapotranspiration, relief, slope and density of drainage channels; (B) Factors contributing to... coal mining operation may affect this alluvial valley floor or waters that supply the alluvial valley... alluvial valley floor that would be affected by the surface coal mining operation is of such small...

  16. Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer salts

    DEFF Research Database (Denmark)

    Sing, M.; Schwingenschlögl, U.; Claessen, R.

    2003-01-01

    We have thoroughly characterized the surfaces of the organic charge-transfer salts TTF-TCNQ and (TMTSF)(2)PF6 which are generally acknowledged as prototypical examples of one-dimensional conductors. In particular x-ray-induced photoemission spectroscopy turns out to be a valuable nondestructive d...

  17. Surface optical phonon-assisted electron Raman scattering in a semiconductor quantum disc

    Institute of Scientific and Technical Information of China (English)

    刘翠红; 马本堃; 陈传誉

    2002-01-01

    We have carried out a theoretical calculation of the differential cross section for the electron Raman scatteringprocess associated with the surface optical phonon modes in a semiconductor quantum disc. Electron states are consid-ered to be confined within a quantum disc with infinite potential barriers. The optical phonon modes we have adoptedare the slab phonon modes by taking into consideration the Frohlich interaction between an electron and a phonon.The selection rules for the Raman process are given. Numerical results and a discussion are also presented for variousradii and thicknesses of the disc, and different incident radiation energies.

  18. Origin of Power Laws for Reactions at Metal Surfaces Mediated by Hot Electrons

    DEFF Research Database (Denmark)

    Olsen, Thomas; Schiøtz, Jakob

    2009-01-01

    A wide range of experiments have established that certain chemical reactions at metal surfaces can be driven by multiple hot-electron-mediated excitations of adsorbates. A high transient density of hot electrons is obtained by means of femtosecond laser pulses and a characteristic feature...... of such experiments is the emergence of a power law dependence of the reaction yield on the laser fluence Y similar to F-n. We propose a model of multiple inelastic scattering by hot electrons which reproduces this power law and the observed exponents of several experiments. All parameters are calculated within...

  19. The Fermi surface and f-valence electron count of UPt3

    Science.gov (United States)

    McMullan, G. J.; Rourke, P. M. C.; Norman, M. R.; Huxley, A. D.; Doiron-Leyraud, N.; Flouquet, J.; Lonzarich, G. G.; McCollam, A.; Julian, S. R.

    2008-05-01

    Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt3. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt3 are localized by correlation effects—agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt3. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.

  20. Numerical analysis of the surface-conduction electron-emitter with a new configuration

    Science.gov (United States)

    Shen, Zhihua; Wang, Xiao; Wu, Shengli; Tian, Jinshou

    2016-04-01

    A new kind of surface-conduction electron-emitter (SCE) with a triangular dielectric layer under the conductive film is proposed. The influences of the vertex angle (𝜃) of the triangular dielectric layer and the anode voltage (Ua) on the electron emission efficiency and the focusing capability have been investigated with the finite integration technique (FIT). The numerical simulation results show that SCE with a small vertex angle guarantees higher electron emission efficiency even with a low anode voltage. But the focusing capability of the electron emitter will get worse when the 𝜃 or Ua becomes too small. Take both the electron emission efficiency and focusing capability into consideration, the structure with a vertex angle (𝜃) between 60∘-100∘ and the anode voltage of 1500V is suggested.

  1. Electron Backscatter Diffraction and Transmission Kikuchi Diffraction Analysis of an Austenitic Stainless Steel Subjected to Surface Mechanical Attrition Treatment and Plasma Nitriding.

    Science.gov (United States)

    Proust, Gwénaëlle; Retraint, Delphine; Chemkhi, Mahdi; Roos, Arjen; Demangel, Clemence

    2015-08-01

    Austenitic 316L stainless steel can be used for orthopedic implants due to its biocompatibility and high corrosion resistance. Its range of applications in this field could be broadened by improving its wear and friction properties. Surface properties can be modified through surface hardening treatments. The effects of such treatments on the microstructure of the alloy were investigated here. Surface Mechanical Attrition Treatment (SMAT) is a surface treatment that enhances mechanical properties of the material surface by creating a thin nanocrystalline layer. After SMAT, some specimens underwent a plasma nitriding process to further enhance their surface properties. Using electron backscatter diffraction, transmission Kikuchi diffraction, energy dispersive spectroscopy, and transmission electron microscopy, the microstructural evolution of the stainless steel after these different surface treatments was characterized. Microstructural features investigated include thickness of the nanocrystalline layer, size of the grains within the nanocrystalline layer, and depth of diffusion of nitrogen atoms within the material.

  2. Modeling micro-porous surfaces for secondary electron emission control to suppress multipactor

    Science.gov (United States)

    Sattler, J. M.; Coutu, R. A.; Lake, R.; Laurvick, T.; Back, T.; Fairchild, S.

    2017-08-01

    This work seeks to understand how the topography of a surface can be engineered to control secondary electron emission (SEE) for multipactor suppression. Two unique, semi-empirical models for the secondary electron yield (SEY) of a micro-porous surface are derived and compared. The first model is based on a two-dimensional (2D) pore geometry. The second model is based on a three-dimensional (3D) pore geometry. The SEY of both models is shown to depend on two categories of surface parameters: chemistry and topography. An important parameter in these models is the probability of electron emissions to escape the surface pores. This probability is shown by both models to depend exclusively on the aspect ratio of the pore (the ratio of the pore height to the pore diameter). The increased accuracy of the 3D model (compared to the 2D model) results in lower electron escape probabilities with the greatest reductions occurring for aspect ratios less than two. In order to validate these models, a variety of micro-porous gold surfaces were designed and fabricated using photolithography and electroplating processes. The use of an additive metal-deposition process (instead of the more commonly used subtractive metal-etch process) provided geometrically ideal pores which were necessary to accurately assess the 2D and 3D models. Comparison of the experimentally measured SEY data with model predictions from both the 2D and 3D models illustrates the improved accuracy of the 3D model. For a micro-porous gold surface consisting of pores with aspect ratios of two and a 50% pore density, the 3D model predicts that the maximum total SEY will be one. This provides optimal engineered surface design objectives to pursue for multipactor suppression using gold surfaces.

  3. Presence of exotic electronic surface states in LaBi and LaSb

    Science.gov (United States)

    Niu, X. H.; Xu, D. F.; Bai, Y. H.; Song, Q.; Shen, X. P.; Xie, B. P.; Sun, Z.; Huang, Y. B.; Peets, D. C.; Feng, D. L.

    2016-10-01

    Extremely high magnetoresistance (XMR) in the lanthanum monopnictides La X (X =Sb ,Bi ) has recently attracted interest in these compounds as candidate topological materials. However, their perfect electron-hole compensation provides an alternative explanation, so the possible role of topological surface states requires verification through direct observation. Our angle-resolved photoemission spectroscopy data reveal multiple Dirac-like surface states near the Fermi level in both materials. Intriguingly, we have observed circular dichroism in both surface and near-surface bulk bands. Thus the spin-orbit-coupling-induced orbital and spin angular momentum textures may provide a mechanism to forbid backscattering in zero field, suggesting that surface and near-surface bulk bands may contribute strongly to XMR in La X . The extremely simple rocksalt structure of these materials and the ease with which high-quality crystals can be prepared suggest that they may be an ideal platform for further investigation of topological matter.

  4. Importance of bulk states for the electronic structure of semiconductor surfaces: implications for finite slabs.

    Science.gov (United States)

    Sagisaka, Keisuke; Nara, Jun; Bowler, David

    2017-04-12

    We investigate the influence of slab thickness on the electronic structure of the Si(1 0 0)- p([Formula: see text]) surface in density functional theory (DFT) calculations, considering both density of states and band structure. Our calculations, with slab thicknesses of up to 78 atomic layers, reveal that the slab thickness profoundly affects the surface band structure, particularly the dangling bond states of the silicon dimers near the Fermi level. We find that, to precisely reproduce the surface bands, the slab thickness needs to be large enough to completely converge the bulk bands in the slab. In the case of the Si(1 0 0) surface, the dispersion features of the surface bands, such as the band shape and width, converge when the slab thickness is larger than 30 layers. Complete convergence of both the surface and bulk bands in the slab is only achieved when the slab thickness is greater than 60 layers.

  5. Electron- and Photon-stimulated Desorption of Alkali Atoms from Lunar Sample and a Model Mineral Surface

    Science.gov (United States)

    Yakshinskiy, B. V.; Madey, T. E.

    2003-01-01

    We report recent results on an investigation of source mechanisms for the origin of alkali atoms in the tenuous planetary atmospheres, with focus on non-thermal processes (photon stimulated desorption (PSD), electron stimulated desorption (ESD), and ion sputtering). Whereas alkaline earth oxides (MgO, CaO) are far more abundant in lunar samples than alkali oxides (Na2O, K2O), the atmosphere of the Moon contains easily measurable concentrations of Na and K, while Ca and Mg are undetected there; traces of Ca have recently been seen in the Moon's atmosphere (10-3 of Na). The experiments have included ESD, PSD and ion sputtering of alkali atoms from model mineral surface (amorphous SiO2) and from a lunar basalt sample obtained from NASA. The comparison is made between ESD and PSD efficiency of monovalent alkalis (Na, K) and divalent alkaline earths (Ba, Ca).The ultrahigh vacuum measurement scheme for ESD and PSD of Na atoms includes a highly sensitive alkali metal detector based on surface ionization, and a time-of-flight technique. For PSD measurements, a mercury arc light source (filtered and chopped) is used. We find that bombardment of the alkali covered surfaces by ultraviolet photons or by low energy electrons (E>4 eV) causes desorption of hot alkali atoms. This results are consistent with the model developed to explain our previous measurements of sodium desorption from a silica surface and from water ice: electron- or photon-induced charge transfer from the substrate to the ionic adsorbate causes formation of a neutral alkali atom in a repulsive configuration, from which desorption occurs. The two-electron charge transfer to cause desorption of divalent alkaline eath ions is a less likely process.The data support the suggestion that PSD by UV solar photons is a dominant source process for alkalis in the tenuous lunar atmosphere.

  6. Adsorption of gaseous hydrocarbons on activated carbon: characteristic kinetic curve. [Includes effect of surface migration on kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Costa, E.; Calleja, G.; Domingo, F.

    1985-06-01

    The internal diffusion coefficients, D /sub i/ , of pure methane, ethane and ethylene as well as some of their binary and ternary mixtures, have been calculated at 20/sup 0/C for solid particles of a commercial activated carbon. It has been observed that the contribution of the surface migration mechanism to the global mass transfer process inside the adsorbent particles can be as much as 70-80%. Values for the surface migration coefficient D /sub s/ have also been calculated from the relation D /sub i/ = D /sub g/ + KD /sub s/ , where K is a dimensionless mean slope factor. Values found for both coefficients are of the same order of magnitude as those reported in the literature for similar systems. All the values for the internal diffusion coefficients of these pure components and their mixtures fit into a single correlation curve, the characteristic kinetic curve of the adsorbent.

  7. Non-vacuum electron-beam carburizing and surface hardening of mild steel

    Science.gov (United States)

    Bataev, I. A.; Golkovskii, M. G.; Losinskaya, A. A.; Bataev, A. A.; Popelyukh, A. I.; Hassel, T.; Golovin, D. D.

    2014-12-01

    In this paper, we study the structure, microhardness, and tribological properties of surface layers of mild (0.19% C) steel, which was formed by electron-beam cladding with an iron-graphite powder mixture followed by quenching and tempering. A 1.4 MeV electron beam that was extracted into air was used. Cladding of steel with the iron-graphite mixture at a beam current of 24 and 26 mA formed a hypoeutectic cast iron layer (2.19% C) and a hypereutectoid steel (1.57% C) layer, which were 2.0 and 2.6 mm thick, respectively. The microhardness of the surface-quenched and tempered steel and cast iron layers was 7 and 8 GPa, respectively. Electron-beam quenching of the surface layers of hypoeutectic cast iron was accompanied with multiple cracking. During the quenching of the 1.57% C steel layer, crack formation was not observed. In friction tests against fixed and loose abrasive particles, the surface layers of hypereutectoid steel and hypoeutectic cast iron that were produced by electron-beam cladding and quenching had lower wear rates than mild steel after pack carburizing, quenching, and tempering. In the sliding wear tests, the cast iron clad layer, which was subjected to electron-beam quenching and tempering, exhibited the highest wear resistance. Electron-beam treatment can be used to harden local areas of large workpieces. It is reasonable to treat clad layers of high-carbon steel with electron-beam quenching and tempering. To prevent multiple cracking, white cast iron layers should not be quenched.

  8. Dynamics of a Rydberg hydrogen atom near a metal surface in the electron-extraction scheme

    Energy Technology Data Exchange (ETDEWEB)

    Iñarrea, Manuel [Área de Física Aplicada, Universidad de La Rioja, Logroño (Spain); Lanchares, Víctor [Departamento de Matemáticas y Computación, Universidad de La Rioja, Logroño, La Rioja (Spain); Palacián, Jesús [Departamento de Ingeniería Matemática e Informática, Universidad Pública de Navarra, Pamplona (Spain); Pascual, Ana I. [Departamento de Matemáticas y Computación, Universidad de La Rioja, Logroño, La Rioja (Spain); Salas, J. Pablo, E-mail: josepablo.salas@unirioja.es [Área de Física Aplicada, Universidad de La Rioja, Logroño (Spain); Yanguas, Patricia [Departamento de Ingeniería Matemática e Informática, Universidad Pública de Navarra, Pamplona (Spain)

    2015-01-23

    We study the classical dynamics of a Rydberg hydrogen atom near a metal surface in the presence of a constant electric field in the electron-extraction situation [1], e.g., when the field attracts the electron to the vacuum. From a dynamical point of view, this field configuration provides a dynamics richer than in the usual ion-extraction scheme, because, depending on the values of field and the atom–surface distance, the atom can be ionized only towards the metal surface, only to the vacuum or to the both sides. The evolution of the phase space structure as a function of the atom–surface distance is explored in the bound regime of the atom. In the high energy regime, the ionization mechanism is also investigated. We find that the classical results of this work are in good agreement with the results obtained in the wave-packet propagation study carried out by So et al. [1]. - Highlights: • We study a classical hydrogen atom near a metal surface plus a electric field. • We explore the phase space structure as a function of the field strength. • We find most of the electronic orbits are oriented along the field direction. • We study the ionization of the atom for several atom–surface distances. • This classical study is in good agreement with the quantum results.

  9. Be(1010): A test ground for surface electron-phonon coupling

    Science.gov (United States)

    Tang, Shu-Jung; Sprunger, Philip; Plummer, Ward; Yang, Wanli; Brouet, Veronique; Zhou, Xingjiang; Shen, Zhi-Xun

    2003-03-01

    The electron-phonon coupling on the Be(10bar10) surface has been investigated with high-resolution photoemission examining temperature dependence and dispersion distortion near the Fermi energy of the two zone boundary surface states. Two surface states (S1 and S2) coexist in a large gap in the bulk projection at the surface zone boundary barA. S1 is localized near the surface in the middle of the gap while S2 is near the bottom band edge and penetrates into the bulk. Using both a Debye and Einstein model to fit the temperature-dependent surface state line width produces an electron-phonon coupling strength with parameters, λ _S1 = 0.647 and λ _S2 = 0.491, more than two times larger than the bulk value, λ _bulk = 0.24. S2 data was measured with a 3D Debye model but the S1 data required an Einstein model with an optical phonon at energy 64 meV. Direct 2D images of the dispersion of the S1 state show dramatic distortion of the electron band dispersion within 64 meV of the Fermi energy. This data is used to extract the real and imaginary parts of the self-energy. Founded by NSF DMR-0105232 and Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725

  10. Various categories of defects after surface alloying induced by high current pulsed electron beam irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Dian [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Tang, Guangze, E-mail: oaktang@hit.edu.cn [School of Material Science & Engineering, Harbin Institute of Technology, Harbin 150001 (China); Ma, Xinxin [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Gu, Le [School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China); Sun, Mingren [School of Material Science & Engineering, Harbin Institute of Technology, Harbin 150001 (China); Wang, Liqin [School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2015-10-01

    Highlights: • Four kinds of defects are found during surface alloying by high current electron beam. • Exploring the mechanism how these defects appear after irradiation. • Increasing pulsing cycles will help to get good surface quality. • Choosing proper energy density will increase surface quality. - Abstract: High current pulsed electron beam (HCPEB) is an attractive advanced materials processing method which could highly increase the mechanical properties and corrosion resistance. However, how to eliminate different kinds of defects during irradiation by HCPEB especially in condition of adding new elements is a challenging task. In the present research, the titanium and TaNb-TiW composite films was deposited on the carburizing steel (SAE9310 steel) by DC magnetron sputtering before irradiation. The process of surface alloying was induced by HCPEB with pulse duration of 2.5 μs and energy density ranging from 3 to 9 J/cm{sup 2}. Investigation of the microstructure indicated that there were several forms of defects after irradiation, such as surface unwetting, surface eruption, micro-cracks and layering. How the defects formed was explained by the results of electron microscopy and energy dispersive spectroscopy. The results also revealed that proper energy density (∼6 J/cm{sup 2}) and multi-number of irradiation (≥50 times) contributed to high quality of alloyed layers after irradiation.

  11. Vibration of bioliquid-filled microtubules embedded in cytoplasm including surface effects using modified couple stress theory.

    Science.gov (United States)

    Ghorbanpour Arani, A; Abdollahian, M; Jalaei, M H

    2015-02-21

    This paper aims to investigate vibrational behavior of bioliquid-filled microtubules (MTs) embedded in cytoplasm considering surface effects. The interactions between the MT, considered as an orthotropic beam within the framework of Euler-Bernoulli beam (EBB) and Timoshenko beam (TB) models, and its surrounding elastic media are simulated by Pasternak foundation model. The modified couple stress theory (MCST) is applied so as to consider the small scale effects while motion equations are derived using energy method and Hamilto's principle for both EBB and TB models. Finally, an analytical method is employed to obtain the frequency of a bioliquid-filled MT, and therefore frequency-response curves are plotted to investigate the influences of small scale parameter, mass density of bioliquid, surface layer and surrounding elastic medium graphically. The results indicate that bioliquid and surface layers play a key role on the frequency of MTs and that the frequency of MTs is decreased with increasing of the mass density of the bioliquid. Vibration analysis of MTs is being considered as a vital problem since MTs look like the nervous system of the biological cells and transmit vibrational signals. It should be noted that the results of this work are hoped to be of use in advanced medical applications especially in the forthcoming use of MTs in transporters for bio-nanosensors.

  12. Interaction potentials for multi-electron atoms in front of a LiF (0 0 1) surface from rainbow scattering

    Energy Technology Data Exchange (ETDEWEB)

    Gravielle, M.S. [Instituto de Astronomía y Física del Espacio (CONICET-UBA), Casilla de correo 67, sucursal 28, C1428EGA Buenos Aires (Argentina); Miraglia, J.E., E-mail: miraglia@iafe.uba.ar [Instituto de Astronomía y Física del Espacio (CONICET-UBA), Casilla de correo 67, sucursal 28, C1428EGA Buenos Aires (Argentina); Schüller, A.; Winter, H. [Institut für Physik, Humboldt Universität zu Berlin, Newtonstrasse 15, D-12489 Berlin-Adlershof (Germany)

    2013-12-15

    Pairwise interaction potentials for multi-electron atoms moving in front of a LiF (0 0 1) surface are investigated theoretically and experimentally. From angular distributions of fast He, N, S, Cl and Kr atoms grazingly scattered under axial surface channeling conditions, rainbow angles are experimentally determined for a wide range of energies for the motion normal to the surface plane. These angles are used as a benchmark to probe the pairwise potential model. In the simulations the scattering process is described by means of the surface eikonal approximation, while the atom–surface interaction is derived by adding binary interatomic potentials that include the proper asymptotic limit.

  13. A Gas-Surface Interaction Model based on Accelerated Reactive Molecular Dynamics for Hypersonic Conditions including Thermal Conduction

    Science.gov (United States)

    2012-02-28

    oxygen interactions with a specific crystalline polymorph of SiO2 (called β- cristobalite ). Computer images of this crystal lattice are shown in Fig. 2...The choice of β- cristobalite is motivated by experimental studies from Balat-Pichelin et al. [15,22,23] where silicon-carbide (SiC) surfaces were...that the measured loss rates correspond to β- cristobalite was based on the fact that for polymorph diagrams of SiO2, β- cristobalite is most stable

  14. Calibration-free quantitative surface topography reconstruction in scanning electron microscopy

    NARCIS (Netherlands)

    Faber, E.T.; Martinez-Martinez, D.; Mansilla, C.; Ocelik, V.; De Hosson, J. Th. M.

    2015-01-01

    This work presents a new approach to obtain reliable surface topography reconstructions from 2D Scanning Electron Microscopy (SEM) images. In this method a set of images taken at different tilt angles are compared by means of digital image correlation (DlC). It is argued that the strength of the met

  15. Low-Frequency Electrostatic Ion Surface Waves in Magnetized Electron-Positron Plasmas

    Science.gov (United States)

    Cho, Sang-Hoon; Lee, Hee J.

    The dispersion relations of a surface ion wave propagating on the interface between a warm electron-positron plasma and vacuum when a static magnetic field is directed either normal to the interface (x-wave) or parallel to the wave vector (z-wave) are solved analytically, and the influence of the magnetic field on the ion surface wave is investigated in detail using some numerical work. It is shown that ion surface waves do not exist if the magnetic field is large enough to make the ion gyrofrequency greater than the ion plasma frequency. The attenuation constant of x-waves is more attenuated than that of z-waves and the x-wave is more attenuated as the parameter normalized ion gyrofrequency ζ increases toward 1, but this tendency is reversed for the z-wave. The z-wave does not exist for k2λD2< (ζ/(1-ζ))(p + 1) while the x-wave exists over the whole range of k, where the fractional number p is the ratio between the unperturbed positron and the electron number density. Additionally, we compare the ion surface wave properties of electron-positron plasma with conventional electron-ion plasma.

  16. Solution of a multiple-scattering inverse problem: electron diffraction from surfaces.

    Science.gov (United States)

    Saldin, D K; Seubert, A; Heinz, K

    2002-03-18

    We present a solution to the multiple-scattering inverse problem for low-energy electron diffraction that enables the determination of the three-dimensional atomic structure of an entire surface unit cell directly from measured data. The solution requires a knowledge of the structure of the underlying bulk crystal and is implemented by a maximum entropy algorithm.

  17. Application of a grating coupler for surface plasmon polariton excitation in a photoemission electron microscopy experiment

    DEFF Research Database (Denmark)

    Leißner, Till; Jauernik, Stephan; Lemke, Christoph

    Surface plasmon polariton (SPP) excitation at a gold-vacuum interface via 800 nm light pulses mediated by a periodic array of gold ridges is probed at high lateral resolution by means of photoemission electron microscopy (PEEM). We directly monitor and quantify the coupling properties as a function...

  18. Extending the range of low energy electron diffraction (LEED) surface structure determination: Co-adsorbed molecules, incommensurate overlayers and alloy surface order studied by new video and electron counting LEED techniques

    Energy Technology Data Exchange (ETDEWEB)

    Ogletree, D.F.

    1986-11-01

    LEED multiple scattering theory is briefly summarized, and aspects of electron scattering with particular significance to experimental measurements such as electron beam coherence, instrument response and phonon scattering are analyzed. Diffuse LEED experiments are discussed. New techniques that enhance the power of LEED are described, including a real-time video image digitizer applied to LEED intensity measurements, along with computer programs to generate I-V curves. The first electron counting LEED detector using a ''wedge and strip'' position sensitive anode and digital electronics is described. This instrument uses picoampere incident beam currents, and its sensitivity is limited only by statistics and counting times. Structural results on new classes of surface systems are presented. The structure of the c(4 x 2) phase of carbon monoxide adsorbed on Pt(111) has been determined, showing that carbon monoxide molecules adsorb in both top and bridge sites, 1.85 +- 0.10 A and 1.55 +- 0.10 A above the metal surface, respectively. The structure of an incommensurate graphite overlayer on Pt(111) is analyzed. The graphite layer is 3.70 +- 0.05 A above the metal surface, with intercalated carbon atoms located 1.25 +- 0.10 A above hollow sites supporting it. The (2..sqrt..3 x 4)-rectangular phase of benzene and carbon monoxide coadsorbed on Pt(111) is analyzed. Benzene molecules adsorb in bridge sites parallel to and 2.10 +- 0.10 A above the surface. The carbon ring is expanded, with an average C-C bond length of 1.72 +- 0.15 A. The carbon monoxide molecules also adsorb in bridge sites. The structure of the (..sqrt..3 x ..sqrt..3) reconstruction on the (111) face of the ..cap alpha..-CuAl alloy has been determined.

  19. Hot-electron-assisted femtochemistry at surfaces: A time-dependent density functional theory approach

    DEFF Research Database (Denmark)

    Gavnholt, Jeppe; Rubio, Angel; Olsen, Thomas;

    2009-01-01

    Using time-evolution time-dependent density functional theory (TDDFT) within the adiabatic local-density approximation, we study the interactions between single electrons and molecular resonances at surfaces. Our system is a nitrogen molecule adsorbed on a ruthenium surface. The surface is modeled...... resonance and the lowering of the resonance energy due to an image charge effect. Finally we apply the TDDFT procedure to only consider the decay of molecular excitations and find that it agrees quite well with the width of the projected density of Kohn-Sham states....

  20. INTERACTION OF SULPHUR WITH BIMETALLIC SURFACES: EFFECTS OF STRUCTURAL, ELECTRONIC AND CHEMICAL PROPERTIES.

    Energy Technology Data Exchange (ETDEWEB)

    RODRIGUEZ,J.A.; HRBEK,J.

    2001-10-04

    In recent years, several new interesting phenomena have been discovered when studying the interaction of sulphur with bimetallic surfaces using the modern techniques of surface science. Very small amounts of sulphur can induce dramatic changes in the morphology of bimetallic surfaces. The electronic perturbations associated with the formation of a heteronuclear metal-metal bond affect the reactivity of the bonded metals toward sulphur. This can be a very important issue to consider when trying to minimize the negative effects of sulphur poisoning or dealing with the design of desulfurization catalysts.

  1. A symmetry-respecting topologically-ordered surface phase of 3d electron topological insulators

    OpenAIRE

    Metlitski, Max A.; Kane, C. L.; Fisher, Matthew P. A.

    2013-01-01

    A 3d electron topological insulator (ETI) is a phase of matter protected by particle-number conservation and time-reversal symmetry. It was previously believed that the surface of an ETI must be gapless unless one of these symmetries is broken. A well-known symmetry-preserving, gapless surface termination of an ETI supports an odd number of Dirac cones. In this paper we deduce a symmetry-respecting, gapped surface termination of an ETI, which carries an intrinsic 2d topological order, Moore-R...

  2. Communication: The correct interpretation of surface hopping trajectories: How to calculate electronic properties

    Energy Technology Data Exchange (ETDEWEB)

    Landry, Brian R.; Falk, Martin J.; Subotnik, Joseph E. [Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, Pennsylvania 19104 (United States)

    2013-12-07

    In a recent paper, we presented a road map for how Tully's fewest switches surface hopping (FSSH) algorithm can be derived, under certain circumstances, from the mixed quantum-classical Liouville equation. In this communication, we now demonstrate how this new interpretation of surface hopping can yield significantly enhanced results for electronic properties in nonadiabatic calculations. Specifically, we calculate diabatic populations for the spin-boson problem using FSSH trajectories. We show that, for some Hamiltonians, without changing the FSSH algorithm at all but rather simply reinterpreting the ensemble of surface hopping trajectories, we recover excellent results and remove any and all ambiguity about the initial condition problem.

  3. 3D scanning electron microscopy applied to surface characterization of fluorosed dental enamel.

    Science.gov (United States)

    Limandri, Silvina; Galván Josa, Víctor; Valentinuzzi, María Cecilia; Chena, María Emilia; Castellano, Gustavo

    2016-05-01

    The enamel surfaces of fluorotic teeth were studied by scanning electron stereomicroscopy. Different whitening treatments were applied to 25 pieces to remove stains caused by fluorosis and their surfaces were characterized by stereomicroscopy in order to obtain functional and amplitude parameters. The topographic features resulting for each treatment were determined through these parameters. The results obtained show that the 3D reconstruction achieved from the SEM stereo pairs is a valuable potential alternative for the surface characterization of this kind of samples. Copyright © 2016 Elsevier Ltd. All rights reserved.

  4. Semiconducting Electronic Property of Graphene Adsorbed on (0001) Surfaces of SiO2

    OpenAIRE

    Cuong, Nguyen Thanh; Otani, Minoru; Okada, Susumu

    2011-01-01

    First-principles total energy calculations are performed to investigate the energetics and electronic structures of graphene adsorbed on both an oxygen-terminated SiO2 (0001) surface and a fully hydroxylated SiO2 (0001) surface. We find that there are several stable adsorption sites for graphene on both O-terminated and hydroxylated SiO2 surfaces. The binding energy in the most stable geometry is found to be 15 meV per C atom, indicating a weak interaction between graphene and SiO2 (0001) sur...

  5. Characterization methodology for pseudomorphic high electron mobility transistors using surface photovoltage spectroscopy

    Science.gov (United States)

    Solodky, S.; Leibovitch, M.; Ashkenasy, N.; Hallakoun, I.; Rosenwaks, Y.; Shapira, Yoram

    2000-12-01

    Pseudomorphic high electron mobility transistor structures have been characterized using surface photovoltage spectroscopy and numerical simulations. According to the effect of the electric fields in different regions of the device on the surface photovoltage spectra, a simple empirical model that correlates the spectral parameters and electrical parameters of the structure has been developed. The spectra and their analysis are shown to provide values for the electrical parameters of the structure. The sensitivity of the technique to the device electrical parameters is shown by three different examples. In these examples, the differences in doping level and surface charge have been monitored as well as the nonuniformity of doping level across the wafer.

  6. Nox diffusion-simulation in an urban area in using the vertical diffusion diagram including a surface roughness parameter

    Energy Technology Data Exchange (ETDEWEB)

    Kono, Hitoshi; Fujimoto, Akira; Nakano, Hiroshi

    1988-03-31

    In recent years, in order to attain a total quantity regulation of air pollution and to prepare a local air-control program, a diffusion simulation is often made using a Gaussian plume model. NOx diffusion simulation of the urban area was carried out using a vertical diffusion width by taking a parameter of ground-surface roughness using Smith's correction to the Gaussian model. For the diffusion of car exhaust gas, comparison was made for the estimate and the measurement by jointly using the values of ground-surface roughness and the initial diffusion width. As a result, change in the diffusion width of the car exhaust gas due to the urban buildings was expressed at a necessary practical level by giving the height of the point of calculation, 1 - 3 m in the central part and 30 cm at the peripheral part, and giving the initial diffusion width of roughly half to equal size of initial diffusion width to the average height of the buildings. (2 figs, 8 tabs, 20 refs)

  7. Oxide/Water Interfaces: How the Surface Chemistry Modifies the Electronic Energy Alignment

    Science.gov (United States)

    Sprik, Michiel

    2014-03-01

    The minimum of the d-electron conduction band of an aqueous transition metal oxide electrode is typically no more than a few 100 mV away from the standard hydrogen electrode (SHE). Because of this favourable alignment of the electronic energy levels (near) metallic transition metal oxides with partly filled d bands can be used as electrocatalysts while the compounds with finite electronic gap can be used as photocatalysts. However, because of their ionic character, transition metal-oxide surfaces also show amphiphilic acid-base activity. At low pH the basic sites are protonated and at high pH the acidic sites deprotonated creating an electrical double layer with corresponding surface potential. The alignment of the electronic energy levels, and by implication their redox activity, is therefore pH dependent. In fact, even in absence of protonic surface charge, the coordination with water molecules is already capable of shifting the electronic energy levels of the oxide by 1 eV or more. Computation of the electronic energies in transition metal oxide electrodes requires therefore a detailed modeling of their aqueous surface chemistry. The solvation energy of the proton is the common energy reference for both redox potentials on the SHE scale and acidity constants (pKa). Computation of the H+ solvation energy is therefore a key component in a unified treatment of redox and acid-base chemistry. In this talk we outline the Density Functional Theory based Molecular Dynamics (DFTMD) method we have developed for this purpose. The central tool of our approach is a method for reversible insertion of protons in the aqueous part of the DFTMD model system. As an illustration we discuss the application to the rutile TiO2/water and MnO2/water interface.

  8. Surface treatment of 0.20% C carbon steel by high-current pulsed electron beam

    Institute of Scientific and Technical Information of China (English)

    XU Guo-cheng; FU Shi-you; GUAN Qing-feng

    2006-01-01

    A high-current pulsed electron beam(HCPEB) generated on the system of Nadezhda-2 was applied to improve the microstructure and performance of 0.20% C low carbon steel. Surface layers of the samples bombarded by explosive electron beam at different pulses was observed by using electron microscopy. The physical model of the thermal-stress process and related modification mechanism as a result of HCPEB irradiation was also investigated. After HCPEB post treatments, obvious changes in microstructure and significant hardening occur in the depth of 200-250 μm from the surface after HCPEB irradiation. Rapid heating and subsequent rapid solidification induce heavy plastic deformation, which results in that the laminated structure of pearlite is substituted by dispersive rounded-like cementites in the near-surface. The effect of HCPEB treatment can reach more than 500 m depth from the surface. The original crystalline structure is changed to a different degree that grows with the numbers of bombardment, and in the surface layer amorphous states and nanocrystaline structures consisting of grains of γ-phase and cementite are found. The violent stress induced by HCPEB irradiation is the origin of the nanostructured and amorphous structure formation.

  9. Excitation of surface plasmon polaritons by electron beam with graphene ribbon arrays

    Science.gov (United States)

    Liu, Yong-Qiang; Liu, Pu-Kun

    2017-03-01

    Graphene has emerged as an alternative material to support surface plasmon polaritons (SPPs) with its excellent properties such as the tight electromagnetic field localization, low dissipative loss, and versatile tunability. Thus, graphene surface plasmon polaritons (GSPs) provide an exciting platform to develop a series of novel devices and systems from the optical band to the terahertz (THz) band. In this paper, theoretical and simulated studies about the excitation of SPPs by an injected electron beam with periodic graphene ribbon arrays deposited on a dielectric medium are presented. The analytical dispersion expression of the GSP mode on the graphene ribbon arrays is obtained by using a modal expansion method along with periodic boundary conditions in the structure. With this result, the dispersion relation, propagation loss, and field pattern of the propagating GSPs for both periodic graphene microribbon arrays and the complete graphene sheet are investigated and analyzed in the THz band. It is shown that the electromagnetic field with a better concentration on the interface can be realized with graphene ribbon arrays compared with the graphene sheet for a given frequency. Besides, the excitation of GSPs by an injected electron beam with graphene ribbon arrays is modeled and implemented by the particle-in-cell simulation based on the finite difference time domain algorithm. GSPs can be excited effectively when the dispersion line of the electron beam and SPPs on the graphene ribbon arrays is matched with each other well. Besides, the dependences of output power on electron beam parameters such as the distance of the electron beam above the graphene ribbon surface and beam voltage are studied and analyzed. Finally, the tunability of graphene conductivity via biased voltage with a ground metal is considered and the tunable excitation of GSPs on the structure with biased drive voltage by the injected electron beam is also realized. The present work can find a

  10. Electronic properties of hydrogen- and oxygen-terminated diamond surfaces exposed to the air

    Institute of Scientific and Technical Information of China (English)

    Liu Feng-Bin; Wang Jia-Dao; Chen Da-Rong; Yan Da-Yun

    2009-01-01

    The electronic properties of hydrogen- and oxygen-terminated diamond surfaces exposed to the air are investigated by scanning probe microscopy (SPM). The results indicate that for the hydrogen-terminated diamond surface a shallow acceptor above the valence-band-maximum (VBM) appears in the band gap. However, the oxygen-terminated diamond film exhibits a high resistivity with a wide band gap. Based on the density-functional-theory, the densities of states, corresponding to molecular adsorbate in hydrogenated and oxygenated diamond (100) surfaces, are studied. The results show that the shallow acceptor in the band gap for the hydrogen-terminated diamond film can be attributed to the interaction between the surface C-H bonding orbitals and the adsorbate molecules, while for the oxygen-terminated diamond film, the interaction between the surface C-O bonding orbitals and the adsorbate molecules can induce occupied states in the valence-band.

  11. Low-energy electron diffraction experiment, theory and surface structure determination

    CERN Document Server

    Hove, Michel A; Chan, Chi-Ming

    1986-01-01

    Surface crystallography plays the same fundamental role in surface science which bulk crystallography has played so successfully in solid-state physics and chemistry. The atomic-scale structure is one of the most important aspects in the understanding of the behavior of surfaces in such widely diverse fields as heterogeneous catalysis, microelectronics, adhesion, lubrication, cor­ rosion, coatings, and solid-solid and solid-liquid interfaces. Low-Energy Electron Diffraction or LEED has become the prime tech­ nique used to determine atomic locations at surfaces. On one hand, LEED has yielded the most numerous and complete structural results to date (almost 200 structures), while on the other, LEED has been regarded as the "technique to beat" by a variety of other surface crystallographic methods, such as photoemission, SEXAFS, ion scattering and atomic diffraction. Although these other approaches have had impressive successes, LEED has remained the most productive technique and has shown the most versatility...

  12. Electronic and magnetic properties of germanene: Surface functionalization and strain effects

    Science.gov (United States)

    Liang, Pei; Liu, Yang; Xing, Song; Shu, Haibo; Tai, Bo

    2016-01-01

    The surface functionalization and strain effects on the structural, electronic, and magnetic properties of full-/half-passivated germanenes are investigated systematically by the first-principle calculations within density functional theory. It is found that the germanenes with full-passivation have different band structures. i.e., the band-gap of GeH is larger than that of GeF and GeCl. Interestingly, when surface passivation and strain are utilized, germanenes go through a transformation from semiconductor to semi-metal. Moreover, germanenes with half-passivation present different magnetic characters, i.e,. Ge2H is a ferromagnetic semiconductor, while Ge2F and Ge2Cl are anti-ferromagnetic semiconductors. The stability of magnetic coupling of Ge2Xs can be modulated by external strain. Our calculations indicate that the electronic and magnetic properties of passivated-germanenes strongly depend on their surface functionalization and strain effects.

  13. Theoretical investigation of the atomic and electronic structure of amino acids on Si(100) surfaces

    Science.gov (United States)

    Luo, Xuan; Qian, Gefei; Sagui, Celeste; Roland, Christopher

    2006-03-01

    There are currently considerable efforts underway to combine silicon-based device technology with myriad of organic molecules, thereby fabricating new structures that take advantage of the tunable electronic and optical properties of organic molecules. A key aspect of this integration process is binding of the organics to the silicon surfaces. As part of this effort, we have been investigating the binding of several amino acids -- the building blocks for proteins -- on the Si (100) surface with state-of-the art density functional theory methods. Specifically, the binding between the buckled Si(100) and the NH2, CH2, COOH, C=0 and NC entities at various surface sites have been investigated. We report and discuss on the resulting structures and their electronic properties.

  14. Atomic force microscopy for the study of specially prepared surfaces including transferred Langmuir-Blodgett layers. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Dr. J. D. Miller

    1999-06-02

    During the past four years a major number of surface science research programs in the Department of Metallurgical Engineering at the University of Utah have involved the use of the Atomic Force Microscope (AFM) and the Langmuir-Blodgett (LB) film balance procured with financial assistance from DOE under grant number DE-FG03-96ER76049. These instruments have been used for research in the areas of nonsulfide flotation chemistry, mineral processing, waste paper deinking, water treatment, treatment of contaminated soil, coal preparation, and plastics recycling. In addition, the AFM and LB film balance have been of great help to university researchers in other departments at the University of Utah and elsewhere, as well as researchers from industry.

  15. MODELING OF THE BUILDING LOCAL PROTECTION (SHELTER – IN PLACE INCLUDING SORBTION OF THE HAZARDOUS CONTAMINANT ON INDOOR SURFACES

    Directory of Open Access Journals (Sweden)

    N. N. Belyayev

    2014-05-01

    Full Text Available Purpose. Chemically hazardous objects, where toxic substances are used, manufactured and stored, and also main lines, on which the hazardous materials transportation is conducted, pose potential sources of atmosphere accidental pollution.Development of the CFD model for evaluating the efficiency of the building local protection from hazardous substantives ingress by using air curtain and sorption/desorption of hazardous substance on indoor surfaces. Methodology. To solve the problem of hydrodynamic interaction of the air curtain with wind flow and considering the building influence on this process the model of ideal fluid is used. In order to calculate the transfer process of the hazardous substance in the atmosphere an equation of convection-diffusion transport of impurities is applied. To calculate the process of indoors air pollution under leaking of foul air Karisson & Huber model is used. This model takes into account the sorption of the hazardous substance at various indoors surfaces. For the numerical integration of the model equations differential methods are used. Findings. In this paper we construct an efficient CFD model of evaluating the effectiveness of the buildings protection against ingress of hazardous substances through the use of an air curtain. On the basis of the built model a computational experiment to assess the effectiveness of this protection method under varying the location of the air curtain relative to the building was carried out. Originality. A new model was developed to compute the effectiveness of the air curtain supply to reduce the toxic chemical concentration inside the building. Practical value. The developed model can be used for design of the building local protection against ingress of hazardous substances.

  16. Preparation of cluster states with trapped electrons on a liquid helium surface

    Institute of Scientific and Technical Information of China (English)

    Ai Ling-Yan; Shi Yan-Li; Zhang Zhi-Ming

    2011-01-01

    We present a scheme for the preparation of one-dimensional (1D) and two-dimensional (2D) cluster states with electrons trapped on a liquid helium surface and driven by a classical laser beam.The two lowest levels of the vertical motion of the electron act as a two-level system,and the quantized vibration of the electron along one of the parallel directions (the x direction) serves as the bosonic mode.The degrees of freedom of the vertical and parallel motions of the trapped electron can be coupled together by a classical laser field.With the proper frequency of the laser field,the cluster states can be realized.

  17. Controlling an electron-transfer reaction at a metal surface by manipulating reactant motion and orientation.

    Science.gov (United States)

    Bartels, Nils; Krüger, Bastian C; Auerbach, Daniel J; Wodtke, Alec M; Schäfer, Tim

    2014-12-08

    The loss or gain of vibrational energy in collisions of an NO molecule with the surface of a gold single crystal proceeds by electron transfer. With the advent of new optical pumping and orientation methods, we can now control all molecular degrees of freedom important to this electron-transfer-mediated process, providing the most detailed look yet into the inner workings of an electron-transfer reaction and showing how to control its outcome. We find the probability of electron transfer increases with increasing translational and vibrational energy as well as with proper orientation of the reactant. However, as the vibrational energy increases, translational excitation becomes unimportant and proper orientation becomes less critical. One can understand the interplay of all three control parameters from simple model potentials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Band structure and Fermi surface of electron-doped C60 monolayers.

    Science.gov (United States)

    Yang, W L; Brouet, V; Zhou, X J; Choi, Hyoung J; Louie, Steven G; Cohen, Marvin L; Kellar, S A; Bogdanov, P V; Lanzara, A; Goldoni, A; Parmigiani, F; Hussain, Z; Shen, Z-X

    2003-04-11

    C60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.

  19. Consequences of plasma oxidation and vacuum annealing on the chemical properties and electron accumulation of In2O3 surfaces

    Science.gov (United States)

    Berthold, Theresa; Rombach, Julius; Stauden, Thomas; Polyakov, Vladimir; Cimalla, Volker; Krischok, Stefan; Bierwagen, Oliver; Himmerlich, Marcel

    2016-12-01

    The influence of oxygen plasma treatments on the surface chemistry and electronic properties of unintentionally doped and Mg-doped In2O3(111) films grown by plasma-assisted molecular beam epitaxy or metal-organic chemical vapor deposition is studied by photoelectron spectroscopy. We evaluate the impact of semiconductor processing technology relevant treatments by an inductively coupled oxygen plasma on the electronic surface properties. In order to determine the underlying reaction processes and chemical changes during film surface-oxygen plasma interaction and to identify reasons for the induced electron depletion, in situ characterization was performed implementing a dielectric barrier discharge oxygen plasma as well as vacuum annealing. The strong depletion of the initial surface electron accumulation layer is identified to be caused by adsorption of reactive oxygen species, which induce an electron transfer from the semiconductor to localized adsorbate states. The chemical modification is found to be restricted to the topmost surface and adsorbate layers. The change in band bending mainly depends on the amount of attached oxygen adatoms and the film bulk electron concentration as confirmed by calculations of the influence of surface state density on the electron concentration and band edge profile using coupled Schrödinger-Poisson calculations. During plasma oxidation, hydrocarbon surface impurities are effectively removed and surface defect states, attributed to oxygen vacancies, vanish. The recurring surface electron accumulation after subsequent vacuum annealing can be consequently explained by surface oxygen vacancies.

  20. High resolution electron energy loss spectroscopy of clean and hydrogen covered Si(001) surfaces: first principles calculations.

    Science.gov (United States)

    Patterson, C H

    2012-09-07

    Surface phonons, conductivities, and loss functions are calculated for reconstructed (2×1), p(2×2) and c(4×2) clean Si(001) surfaces, and (2×1) H and D covered Si(001) surfaces. Surface conductivities perpendicular to the surface are significantly smaller than conductivities parallel to the surface. The surface loss function is compared to high resolution electron energy loss measurements. There is good agreement between calculated loss functions and experiment for H and D covered surfaces. However, agreement between experimental data from different groups and between theory and experiment is poor for clean Si(001) surfaces. Formalisms for calculating electron energy loss spectra are reviewed and the mechanism of electron energy losses to surface vibrations is discussed.

  1. Correlation between morphology, electron band structure, and resistivity of Pb atomic chains on the Si(5 5 3)-Au surface.

    Science.gov (United States)

    Jałochowski, M; Kwapiński, T; Łukasik, P; Nita, P; Kopciuszyński, M

    2016-07-20

    Structural and electron transport properties of multiple Pb atomic chains fabricated on the Si(5 5 3)-Au surface are investigated using scanning tunneling spectroscopy, reflection high electron energy diffraction, angular resolved photoemission electron spectroscopy and in situ electrical resistance. The study shows that Pb atomic chains growth modulates the electron band structure of pristine Si(5 5 3)-Au surface and hence changes its sheet resistivity. Strong correlation between chains morphology, electron band structure and electron transport properties is found. To explain experimental findings a theoretical tight-binding model of multiple atomic chains interacting on effective substrate is proposed.

  2. Density matrix treatment of non-adiabatic photoinduced electron transfer at a semiconductor surface.

    Science.gov (United States)

    Micha, David A

    2012-12-14

    Photoinduced electron transfer at a nanostructured surface leads to localized transitions and involves three different types of non-adiabatic couplings: vertical electronic transitions induced by light absorption emission, coupling of electronic states by the momentum of atomic motions, and their coupling due to interactions with electronic density fluctuations and vibrational motions in the substrate. These phenomena are described in a unified way by a reduced density matrix (RDM) satisfying an equation of motion that contains dissipative rates. The RDM treatment is used here to distinguish non-adiabatic phenomena that are localized from those due to interaction with a medium. The fast decay of localized state populations due to electronic density fluctuations in the medium has been treated within the Lindblad formulation of rates. The formulation is developed introducing vibronic states constructed from electron orbitals available from density functional calculations, and from vibrational states describing local atomic displacements. Related ab initio molecular dynamics calculations have provided diabatic momentum couplings between excited electronic states. This has been done in detail for an indirect photoexcitation mechanism of the surface Ag(3)Si(111):H, which leads to long lasting electronic charge separation. The resulting coupled density matrix equations are solved numerically to obtain the population of the final charge-separated state as it changes over time, for several values of the diabatic momentum coupling. New insight and unexpected results are presented here which can be understood in terms of photoinduced non-adiabatic transitions involving many vibronic states. It is found that the population of long lasting charge separation states is larger for smaller momentum coupling, and that their population grows faster for smaller coupling.

  3. Wettability modification of human tooth surface by water and UV and electron-beam radiation

    Energy Technology Data Exchange (ETDEWEB)

    Tiznado-Orozco, Gaby E., E-mail: gab0409@gmail.com [UMET, Bâtiment C6, Université de Lille 1, Sciences et Technologies, 59650 Villeneuve d' Ascq (France); Unidad Académica de Odontología, Universidad Autónoma de Nayarit, Edificio E7, Ciudad de la Cultura “Amado Nervo”, C.P. 63190 Tepic, Nayarit (Mexico); Reyes-Gasga, José, E-mail: jreyes@fisica.unam.mx [UMET, Bâtiment C6, Université de Lille 1, Sciences et Technologies, 59650 Villeneuve d' Ascq (France); Instituto de Física, UNAM, Circuito de la Investigación s/n, Ciudad Universitaria, 04510 Coyoacan, México, D.F. (Mexico); Elefterie, Florina, E-mail: elefterie_florina@yahoo.com [UMET, Bâtiment C6, Université de Lille 1, Sciences et Technologies, 59650 Villeneuve d' Ascq (France); Beyens, Christophe, E-mail: christophe.beyens@ed.univ-lille1.fr [UMET, Bâtiment C6, Université de Lille 1, Sciences et Technologies, 59650 Villeneuve d' Ascq (France); Maschke, Ulrich, E-mail: Ulrich.Maschke@univ-lille1.fr [UMET, Bâtiment C6, Université de Lille 1, Sciences et Technologies, 59650 Villeneuve d' Ascq (France); Brès, Etienne F., E-mail: etienne.bres@univ-lille1.fr [UMET, Bâtiment C6, Université de Lille 1, Sciences et Technologies, 59650 Villeneuve d' Ascq (France)

    2015-12-01

    The wettability of the human tooth enamel and dentin was analyzed by measuring the contact angles of a drop of distilled water deposited on the surface. The samples were cut along the transverse and longitudinal directions, and their surfaces were subjected to metallographic mirror-finish polishing. Some samples were also acid etched until their microstructure became exposed. Wettability measurements of the samples were done in dry and wet conditions and after ultraviolet (UV) and electron beam (EB) irradiations. The results indicate that water by itself was able to increase the hydrophobicity of these materials. The UV irradiation momentarily reduced the contact angle values, but they recovered after a short time. EB irradiation raised the contact angle and maintained it for a long time. Both enamel and dentin surfaces showed a wide range of contact angles, from approximately 10° (hydrophilic) to 90° (hydrophobic), although the contact angle showed more variability on enamel than on dentin surfaces. Whether the sample's surface had been polished or etched did not influence the contact angle value in wet conditions. - Highlights: • Human tooth surface wettability changes in dry/wet and UV/EB radiation conditions. • More variability in contact angle is observed on enamel than on dentin surfaces. • Water by itself increases the hydrophobicity of the human tooth surface. • UV irradiation reduces momentarily the human tooth surface hydrophobicity. • EB irradiation increases and maintains the hydrophobicity for a long time.

  4. Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals

    Science.gov (United States)

    White, Gaye F.; Shi, Zhi; Shi, Liang; Wang, Zheming; Dohnalkova, Alice C.; Marshall, Matthew J.; Fredrickson, James K.; Zachara, John M.; Butt, Julea N.; Richardson, David J.; Clarke, Thomas A.

    2013-04-01

    The mineral-respiring bacterium Shewanella oneidensis uses a protein complex, MtrCAB, composed of two decaheme cytochromes, MtrC and MtrA, brought together inside a transmembrane porin, MtrB, to transport electrons across the outer membrane to a variety of mineral-based electron acceptors. A proteoliposome system containing a pool of internalized electron carriers was used to investigate how the topology of the MtrCAB complex relates to its ability to transport electrons across a lipid bilayer to externally located Fe(III) oxides. With MtrA facing the interior and MtrC exposed on the outer surface of the phospholipid bilayer, the established in vivo orientation, electron transfer from the interior electron carrier pool through MtrCAB to solid-phase Fe(III) oxides was demonstrated. The rates were 103 times higher than those reported for reduction of goethite, hematite, and lepidocrocite by S. oneidensis, and the order of the reaction rates was consistent with those observed in S. oneidensis cultures. In contrast, established rates for single turnover reactions between purified MtrC and Fe(III) oxides were 103 times lower. By providing a continuous flow of electrons, the proteoliposome experiments demonstrate that conduction through MtrCAB directly to Fe(III) oxides is sufficient to support in vivo, anaerobic, solid-phase iron respiration.

  5. Electron dynamics in the normal state of cuprates: Spectral function, Fermi surface and ARPES data

    Science.gov (United States)

    Zubov, E. E.

    2016-11-01

    An influence of the electron-phonon interaction on excitation spectrum and damping in a narrow band electron subsystem of cuprates has been investigated. Within the framework of the t-J model an approach to solving a problem of account of both strong electron correlations and local electron-phonon binding with characteristic Einstein mode ω0 in the normal state has been presented. In approximation Hubbard-I it was found an exact solution for the polaron bands. We established that in the low-dimensional system with a pure kinematic part of Hamiltonian a complicated excitation spectrum is realized. It is determined mainly by peculiarities of the lattice Green's function. In the definite area of the electron concentration and hopping integrals a correlation gap may be possible on the Fermi level. Also, in specific cases it is observed a doping evolution of the Fermi surface. We found that the strong electron-phonon binding enforces a degree of coherence of electron-polaron excitations near the Fermi level and spectrum along the nodal direction depends on wave vector module weakly. It corresponds to ARPES data. A possible origin of the experimentally observed kink in the nodal direction of cuprates is explained by fine structure of the polaron band to be formed near the mode -ω0.

  6. Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches

    Energy Technology Data Exchange (ETDEWEB)

    Ramakrishnan, Raghunathan, E-mail: r.ramakrishnan@unibas.ch [Institute of Physical Chemistry, National Center for Computational Design and Discovery of Novel Materials (MARVEL), Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel (Switzerland); Nest, Mathias [Theoretische Chemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching (Germany)

    2015-01-13

    Highlights: • We model electron dynamics across cyano alkanethiolates attached to gold cluster. • We present electron transfer time scales from TD-DFT and TD-CI based simulations. • Both DFT and CI methods qualitatively predict the trend in time scales. • TD-CI predicts the experimental relative time scale very accurately. - Abstract: We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual π{sup ∗} molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

  7. Localized electronic states at grain boundaries on the surface of graphene and graphite

    Science.gov (United States)

    Luican-Mayer, Adina; Barrios-Vargas, Jose E.; Toft Falkenberg, Jesper; Autès, Gabriel; Cummings, Aron W.; Soriano, David; Li, Guohong; Brandbyge, Mads; Yazyev, Oleg V.; Roche, Stephan; Andrei, Eva Y.

    2016-09-01

    Recent advances in large-scale synthesis of graphene and other 2D materials have underscored the importance of local defects such as dislocations and grain boundaries (GBs), and especially their tendency to alter the electronic properties of the material. Understanding how the polycrystalline morphology affects the electronic properties is crucial for the development of applications such as flexible electronics, energy harvesting devices or sensors. We here report on atomic scale characterization of several GBs and on the structural-dependence of the localized electronic states in their vicinity. Using low temperature scanning tunneling microscopy and spectroscopy, together with tight binding and ab initio numerical simulations we explore GBs on the surface of graphite and elucidate the interconnection between the local density of states and their atomic structure. We show that the electronic fingerprints of these GBs consist of pronounced resonances which, depending on the relative orientation of the adjacent crystallites, appear either on the electron side of the spectrum or as an electron-hole symmetric doublet close to the charge neutrality point. These two types of spectral features will impact very differently the transport properties allowing, in the asymmetric case to introduce transport anisotropy which could be utilized to design novel growth and fabrication strategies to control device performance.

  8. Kiwi fruit (Actinidia chinensis) quality determination based on surface acoustic wave resonator combined with electronic nose.

    Science.gov (United States)

    Wei, Liu; Guohua, Hui

    2015-01-01

    In this study, electronic nose (EN) combined with a 433 MHz surface acoustic wave resonator (SAWR) was used to determine Kiwi fruit quality under 12-day storage. EN responses to Kiwi samples were measured and analyzed by principal component analysis (PCA) and stochastic resonance (SR) methods. SAWR frequency eigen values were also measured to predict freshness. Kiwi fruit sample's weight loss index and human sensory evaluation were examined to characteristic its quality and freshness. Kiwi fruit's quality predictive models based on EN, SAWR, and EN combined with SAWR were developed, respectively. Weight loss and human sensory evaluation results demonstrated that Kiwi fruit's quality decline and overall acceptance decrease during the storage. Experiment result indicated that the PCA method could qualitatively discriminate all Kiwi fruit samples with different storage time. Both SR and SAWR frequency analysis methods could successfully discriminate samples with high regression coefficients (R = 0.98093 and R = 0.99014, respectively). The validation experiment results showed that the mixed predictive model developed using EN combined with SAWR present higher quality prediction accuracy than the model developed either by EN or by SAWR. This method exhibits some advantages including high accuracy, non-destructive, low cost, etc. It provides an effective way for fruit quality rapid analysis.

  9. Direct first-principles simulation of a high-performance electron emitter: Lithium-oxide-coated diamond surface

    Energy Technology Data Exchange (ETDEWEB)

    Miyamoto, Yoshiyuki, E-mail: yoshi-miyamoto@aist.go.jp; Miyazaki, Takehide [Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Takeuchi, Daisuke; Yamasaki, Satoshi [Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); JST, ALCA, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)

    2014-09-28

    We examined the field emission properties of lithium(Li)/oxygen(O)-co-terminated diamond (001) surface [C(001)-LiO] through real-time electron dynamics simulation under an applied field. The current emitted from this surface was found to be more than four-fold that emitted by an H-terminated (001) surface, the latter being a typical negative electron affinity system. This high performance is attributed to the Li layer, which bends the potential wall of O-induced electron pockets down in the direction of vacuum, thus facilitating electron emission. Detailed analysis of the emitted electrons and the profile of the self-consistent potential elucidated that the role of O atoms changes from an electron barrier on OH-terminated diamond surfaces to an outlet for electron emission on C(001)-LiO.

  10. Surface Nanocrystallization of 3Cr13 Stainless Steel Induced by High-Current Pulsed Electron Beam Irradiation

    OpenAIRE

    2013-01-01

    The nanocrystalline surface was produced on 3Cr13 martensite stainless steel surface using high-current pulsed electron beam (HCPEB) technique. The structures of the nanocrystallized surface were characterized by X-ray diffraction and electron microscopy. Two nanostructures consisting of fine austenite grains (50–150 nm) and very fine carbides precipitates are formed in melted surface layer after multiple bombardments via dissolution of carbides and crater eruption. It is demonstrated that th...

  11. Surface Potential Control on Thin Oxide Films with Respect to Electron Stimulated Desorption Studies

    Science.gov (United States)

    Bernheim, Marc; Rousse, Gilles

    1995-09-01

    These experiments deal with the study of desorption of negative ions stimulated by low energy electron collisions on insulating surfaces covered with various adsorbates. For such investigation a careful control of the sample surface potential is required to set the incident electron energy accurately as well as to identify the desorbed species by mass spectrometry. Most of the reported experiments concern this surface potential control. We show that, for very thin SiO2 films thermally grown on silicon substrates, a tunnel conduction might set the surface potential accurately. This assertion mainly relies on recording the intensity of electrons transmitted through thin oxides as well as the intensity of backscattered and secondary electrons re-emitted from the surface. A direct comparison of the O^- ion energy distributions confirms the correct control of the surface potential for a large range of incident electron energies. In such condition we noticed that the O^- desorption yields just swiftly varied with incident electron energy. In particular no modification could be detected as the incident electron energy passed the various Auger excitation levels. The discrepancy between this last result and the published data is discussed in the last part of this paper. Des collisions électroniques sur des surfaces peuvent provoquer une éjection d'ions négatifs formés à partir des molécules adsorbées suivant un processus résonnant à très basse énergie. Pour étendre ces études expérimentales aux surfaces isolantes, un contrôle précis du potentiel superficiel devient indispensable tant pour fixer l'énergie finale des électrons sur la surface que pour effectuer la spectrométrie des ions désorbés. L'examen de surfaces de silice en couche mince montre comment une conduction tunnel intervient pour fixer le potentiel des surfaces examinées. Ces travaux expérimentaux effectués dans une configuration de miroir électrostatique reposent principalement sur l

  12. A first principles investigation of electron transfer between Fe(II) and U(VI) on insulating Al- vs. semiconducting Fe-oxide surfaces via the proximity effect

    Science.gov (United States)

    Taylor, S. D.; Marcano, M. C.; Becker, U.

    2017-01-01

    This study investigates how the intrinsic chemical and electronic properties of mineral surfaces and their associated electron transfer (ET) pathways influence the reduction of U(VI) by surface-associated Fe(II). Density functional theory (DFT), including the Hubbard U correction to the exchange-correlation functional, was used to investigate sorption/redox reactions and ET mechanisms between Fe(II) and U(VI) coadsorbed on isostructural, periodic (0 0 1) surfaces of the insulator corundum (α-Al2O3) vs. the semiconductor hematite (α-Fe2O3). Furthermore, the coadsorbed Fe(II) and U(VI) ions are spatially separated from one another on the surfaces (⩾5.9 Å) to observe whether electronic-coupling through the semiconducting hematite surface facilitates ET between the adsorbates, a phenomenon known as the proximity effect. The calculations show that the different chemical and electronic properties between the isostructural corundum and hematite (0 0 1) surfaces lead to considerably different ET mechanisms between Fe(II) and U(VI). ET on the insulating corundum (0 0 1) surface is limited by the adsorbates' structural configuration. When Fe(II) and U(VI) are spatially separated and do not directly interact with one another (e.g. via an inner-sphere complex), U(VI) reduction by Fe(II) cannot occur as there is no physical pathway enabling ET between the adsorbates. In contrast to the insulating corundum (0 0 1) surface, the hematite (0 0 1) surface can potentially participate in ET reactions due to the high number of electron acceptor sites from the Fe d-states near the Fermi level at the hematite surface. The adsorption of Fe(II) also introduces d-states near the Fermi level as well as shifts unoccupied d-states of the Fe cations at the hematite surface to lower energies, making the surface more conductive. In turn, electronic coupling through the surface can link the spatially separated adsorbates to one another and provide distinct ET pathways for an electron from Fe

  13. Benzene derivatives adsorbed to the Ag(111) surface: Binding sites and electronic structure

    Science.gov (United States)

    Miller, Daniel P.; Simpson, Scott; Tymińska, Nina; Zurek, Eva

    2015-03-01

    Dispersion corrected Density Functional Theory calculations were employed to study the adsorption of benzenes derivatized with functional groups encompassing a large region of the activated/deactivated spectrum to the Ag(111) surface. Benzenes substituted with weak activating or deactivating groups, such as methyl and fluoro, do not have a strong preference for adsorbing to a particular site on the substrate, with the corrugations in the potential energy surface being similar to those of benzene. Strong activating (N(CH3)2) and deactivating (NO2) groups, on the other hand, possess a distinct site preference. The nitrogen in the former prefers to lie above a silver atom (top site), but in the latter a hollow hexagonal-closed-packed (Hhcp) site of the Ag(111) surface is favored instead. Benzenes derivatized with classic activating groups donate electron density from their highest occupied molecular orbital to the surface, and those functionalized with deactivating groups withdraw electron density from the surface into orbitals that are unoccupied in the gas phase. For benzenes functionalized with two substituents, the groups that are strongly activating or deactivating control the site preference and the other groups assume sites that are, to a large degree, dictated by their positions on the benzene ring. The relative stabilities of the ortho, meta, and para positional isomers of disubstituted benzenes can, in some cases, be modified by adsorption to the surface.

  14. Atomic and electronic structure of molybdenum carbide phases: bulk and low Miller-index surfaces.

    Science.gov (United States)

    Politi, José Roberto dos Santos; Viñes, Francesc; Rodriguez, Jose A; Illas, Francesc

    2013-08-14

    The geometric and electronic structure of catalytically relevant molybdenum carbide phases (cubic δ-MoC, hexagonal α-MoC, and orthorhombic β-Mo2C) and their low Miller-index surfaces have been investigated by means of periodic density functional theory (DFT) based calculations with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. Comparison to available experimental data indicates that this functional is particularly well suited to study these materials. The calculations reveal that β-Mo2C has a stronger metallic character than the other two polymorphs, both β-Mo2C and δ-MoC have a large ionic contribution, and δ- and α-MoC exhibit the strongest covalent character. Among the various surfaces explored, the calculations reveal the high stability of the δ-MoC(001) nonpolar surface, Mo- and C-terminated (001) polar surfaces of α-MoC, and the nonpolar (011) surface of β-Mo2C. A substantially low work function of only 3.4 eV is predicted for β-Mo2C(011), suggesting that this system is particularly well suited for (electro)catalytic processes where surface → adsorbate electron transfer is essential. The overall implications for heterogeneously catalysed reactions by these molybdenum carbide nanoparticles are also discussed.

  15. New electronics for the surface detectors of the Pierre Auger Observatory

    Science.gov (United States)

    Kleifges, M.; Pierre Auger Collaboration

    2016-07-01

    The Pierre Auger Observatory is the largest installation worldwide for the investigation of ultra-high energy cosmic rays. Air showers are detected using a hybrid technique with 27 fluorescence telescopes and 1660 water-Cherenkov detectors (WCD) distributed over about 3000 km2. The Auger Collaboration has decided to upgrade the electronics of the WCD and complement the surface detector with scintillators (SSD). The objective is to improve the separation between the muonic and the electron/photon shower component for better mass composition determination during an extended operation period of 8-10 years. The surface detector electronics records data locally and generates time stamps based on the GPS timing. The performance of the detectors is significantly improved with a higher sampling rate, an increased dynamic range, new generation of GPS receivers, and FPGA integrated CPU power. The number of analog channels will be increased to integrate the new SSD, but the power consumption needs to stay below 10 W to be able to use the existing photovoltaic system. In this paper, the concept of the additional SSD is presented with a focus on the design and performance of the new surface detector electronics.

  16. New electronics for the surface detectors of the Pierre Auger Observatory

    Energy Technology Data Exchange (ETDEWEB)

    Kleifges, M., E-mail: Matthias.Kleifges@kit.edu [Karlsruhe Institute of Technology – Institute for Data Processing and Electronics, Karlsruhe (Germany)

    2016-07-11

    The Pierre Auger Observatory is the largest installation worldwide for the investigation of ultra-high energy cosmic rays. Air showers are detected using a hybrid technique with 27 fluorescence telescopes and 1660 water-Cherenkov detectors (WCD) distributed over about 3000 km{sup 2}. The Auger Collaboration has decided to upgrade the electronics of the WCD and complement the surface detector with scintillators (SSD). The objective is to improve the separation between the muonic and the electron/photon shower component for better mass composition determination during an extended operation period of 8–10 years. The surface detector electronics records data locally and generates time stamps based on the GPS timing. The performance of the detectors is significantly improved with a higher sampling rate, an increased dynamic range, new generation of GPS receivers, and FPGA integrated CPU power. The number of analog channels will be increased to integrate the new SSD, but the power consumption needs to stay below 10 W to be able to use the existing photovoltaic system. In this paper, the concept of the additional SSD is presented with a focus on the design and performance of the new surface detector electronics.

  17. PE and IPE study of the surface electronic structure of Y(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Stolwijk, Sebastian D.; Budke, Michael; Donath, Markus [Physikalisches Institut, Westfaelische Wilhelms-Universitaet Muenster (Germany); Doebrich, Kristian M. [Fachbereich Physik, Freie Universitaet Berlin (Germany)

    2009-07-01

    Yttrium and gadolinium are isoelectronic elements with respect to their valence bands but differ in their magnetic properties due to the additional 4f electrons in Gd. Therefore, Y may be viewed as paramagnetic model for ferromagnetic Gd. A comparative study of the electronic structure of Y and Gd promises to reveal electronic properties that are directly linked to ferromagnetism. For more than 20 years, differences in the photoemission spectra of Y(0001) obtained from single-crystalline bulk samples and thin films grown on W(110) have remained an unsolved puzzle. Our recent study on the (0001) surface of a single-crystalline yttrium bulk sample shows that most of the spectral features arise due to impurities such as carbon, chlorine, oxygen and hydrogen. In order to develop a consistent picture of the surface electronic structure of Y(0001), we compare direct and inverse-photoemission results from single-crystalline yttrium bulk samples and ultrathin films, particularly with regard to the surface state close to the Fermi level. These results are discussed in view of data obtained for Gd.

  18. Ultrafast Electron Transfer Between Dye and Catalyst on a Mesoporous NiO Surface.

    Science.gov (United States)

    Brown, Allison M; Antila, Liisa J; Mirmohades, Mohammad; Pullen, Sonja; Ott, Sascha; Hammarström, Leif

    2016-07-01

    The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)6 (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (τ ≈ 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t1/2 ≈ 10 ps) and efficient surface electron transfer from C343(-) to the coadsorbed [FeFe](mcbdt)(CO)6. The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on DSSFDs.

  19. Real-Space Imaging of Carrier Dynamics of Materials Surfaces by Second-Generation Four-Dimensional Scanning Ultrafast Electron Microscopy

    KAUST Repository

    Sun, Jingya

    2015-09-14

    In the fields of photocatalysis and photovoltaics, ultrafast dynamical processes, including carrier trapping and recombination on material surfaces, are among the key factors that determine the overall energy conversion efficiency. A precise knowledge of these dynamical events on the nanometer (nm) and femtosecond (fs) scales was not accessible until recently. The only way to access such fundamental processes fully is to map the surface dynamics selectively in real space and time. In this study, we establish a second generation of four-dimensional scanning ultrafast electron microscopy (4D S-UEM) and demonstrate the ability to record time-resolved images (snapshots) of material surfaces with 650 fs and ∼5 nm temporal and spatial resolutions, respectively. In this method, the surface of a specimen is excited by a clocking optical pulse and imaged using a pulsed primary electron beam as a probe pulse, generating secondary electrons (SEs), which are emitted from the surface of the specimen in a manner that is sensitive to the local electron/hole density. This method provides direct and controllable information regarding surface dynamics. We clearly demonstrate how the surface morphology, grains, defects, and nanostructured features can significantly impact the overall dynamical processes on the surface of photoactive-materials. In addition, the ability to access two regimes of dynamical probing in a single experiment and the energy loss of SEs in semiconductor-nanoscale materials will also be discussed.

  20. Fractography of Fatigue Fracture Surface in Silumin Subjected to Electron-Beam Processing

    Science.gov (United States)

    Konovalov, S. V.; Aksenova, K. V.; Gromov, V. E.; Ivanov, Yu F.; Semina, O. A.

    2016-08-01

    The surface modification of the eutectic silumin with high-intensity pulsed electron beam has been carried out. Multi-cycle fatigue tests were performed and irradiation mode made possible the increase in the silumin fatigue life more than 3.5 times was determined. Studies of the structure of the surface irradiation and surface fatigue fracture of silumin in the initial (unirradiated) state and after modification with intense pulsed electron beam were carried out by methods of scanning electron microscopy. It has been shown, that in mode of partial melting of the irradiation surface the modification process of silicon plates is accompanied by the formation of numerous large micropores along the boundary plate/matrix and microcracks located in the silicon plates. A multi-modal structure (grain size within 30-50 μm with silicon particles up to 10 μm located on the boundaries) is formed in stable melting mode, as well as subgrain structure in the form of crystallization cells from 100 to 250 μm in size). Formation of a multi-modal, multi-phase, submicro- and nanosize structure assisting to a significant increase in the critical length of the crack, the safety coefficient and decrease in step of cracks for loading cycle was the main cause for the increase in silumin fatigue life.

  1. Surface Nanostructure Formations in an AISI 316L Stainless Steel Induced by Pulsed Electron Beam Treatment

    Directory of Open Access Journals (Sweden)

    Yang Cai

    2015-01-01

    Full Text Available High current pulsed electron beam (HCPEB is an efficient technique for surface modifications of metallic materials. In the present work, the formations of surface nanostructures in an AISI 316L stainless steel induced by direct HCPEB treatment and HCPEB alloying have been investigated. After HCPEB Ti alloying, the sample surface contained a mixture of the ferrite and austenite phases with an average grain size of about 90 nm, because the addition of Ti favors the formation of ferrite. In contrast, electron backscattered diffraction (EBSD analyses revealed no structural refinement on the direct HCPEB treated sample. However, transmission electron microscope (TEM observations showed that fine cells having an average size of 150 nm without misorientations, as well as nanosized carbide particles, were formed in the surface layer after the direct HCPEB treatment. The formation of nanostructures in the 316L stainless steel is therefore attributed to the rapid solidification and the generation of different phases other than the steel substrate in the melted layer.

  2. Demonstration of Surface Electron Rejection with Interleaved Germanium Detectors for Dark Matter Search

    CERN Document Server

    Agnese, R; Balakishiyeva, D; Thakur, R Basu; Bauer, D A; Borgland, A; Brandt, D; Brink, P L; Bunker, R; Cabrera, B; Caldwell, D O; Cerdeno, D G; Chagani, H; Cherry, M; Cooley, J; Cornell, B; Crewdson, C H; Cushman, P; Daal, M; Di Stefano, P C F; Silva, E Do Couto E; Doughty, T; Esteban, L; Fallows, S; Figueroa-Feliciano, E; Fox, J; Fritts, M; Godfrey, G L; Golwala, S R; Hall, J; Harris, H R; Hasi, J; Hertel, S A; Hines, B A; Hofer, T; Holmgren, D; Hsu, L; Huber, M E; Jastram, A; Kamaev, O; Kara, B; Kelsey, M H; Kenany, S A; Kennedy, A; Kenney, C J; Kiveni, M; Koch, K; Loer, B; Asamar, E Lopez; Mahapatra, R; Mandic, V; Martinez, C; McCarthy, K A; Mirabolfathi, N; Moffatt, R A; Moore, D C; Nadeau, P; Nelson, R H; Novak, L; Page, K; Partridge, R; Pepin, M; Phipps, A; Prasad, K; Pyle, M; Qiu, H; Radpour, R; Rau, W; Redl, P; Reisetter, A; Resch, R W; Ricci, Y; Saab, T; Sadoulet, B; Sander, J; Schmitt, R; Schneck, K; Schnee, R W; Scorza, S; Seitz, D; Serfass, B; Shank, B; Speller, D; Tomada, A; Villano, A N; Welliver, B; Wright, D H; Yellin, S; Yen, J J; Young, B A; Zhang, J

    2013-01-01

    SuperCDMS, a direct search for WIMPs, is currently operating a 9-kg array of cryogenic germanium (Ge) detectors in the Soudan Underground Laboratory. These detectors, known as iZIPs, use ionization and phonon sensors placed symmetrically on both sides of a Ge crystal to measure both charge and athermal phonons from each particle interaction. The information from each event provides excellent discrimination between electron recoils and nuclear recoils, as well as discrimination between events on the detector surface and those in the interior. To demonstrate the surface electron rejection capabilities, two $^{210}$Pb sources were installed facing detectors, producing $\\sim$130 beta decays/hr. In $\\sim$800 live hours, no events leaked into the WIMP signal region in the recoil energy range 8--115 keVr, providing an upper limit to the surface event leakage fraction of $1.7 \\times 10^{-5}$ at 90% C.L. This rejection factor demonstrates that surface electrons would produce $< 0.6$ event background in the 0.3 ton-...

  3. Electron coincidence studies of sulfur-overlayers on Cu(001) and Ni(001) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Di Filippo, G., E-mail: gianluca.filippo@fau.de [Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany); Schumann, F.O.; Patil, S.; Wei, Z. [Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany); Stefani, G. [CNISM and Dipartimento di Scienze, Università Roma Tre, Via della Vasca Navale 84, 00146 Rome (Italy); Fratesi, G. [Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milan (Italy); Trioni, M.I. [CNR – National Research Council of Italy, ISTM, Via Golgi 19, 20133 Milan (Italy); Kirschner, J. [Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany)

    2016-08-15

    Highlights: • The LVV Auger decay of different sulfur-overlayers is investigated. • The decay can be described within a two-step model. • The Auger line shapes furnish information on the electronic structure at the surface. • The e–e correlation energy is hardly affected by coverage or substrate variations. - Abstract: We have prepared different sulfur-overlayers on Cu(001) and Ni(001) surfaces which differ in their coverage and local environment of the S adatoms. Via photon absorption we excited the S 2p level and studied the subsequent Auger decay with a coincidence spectrometer. We discuss the variation of the coincidence rate as a function of the energy sum of the photo-Auger electron pair. This is linked to the binding energy of the double-hole state. We find that the photon energy has no dramatic influence on the spectra. Differences are observed when the local environment of sulfur is changed. The observed spectral changes are mainly ascribable to the variation of the density of states at the different surfaces. On the contrary, the strength of electron–electron correlation at the surface states is hardly affected by coverage or substrate variation.

  4. Electron collisions with atoms, ions, molecules, and surfaces: Fundamental science empowering advances in technology

    Science.gov (United States)

    Bartschat, Klaus; Kushner, Mark J.

    2016-06-01

    Electron collisions with atoms, ions, molecules, and surfaces are critically important to the understanding and modeling of low-temperature plasmas (LTPs), and so in the development of technologies based on LTPs. Recent progress in obtaining experimental benchmark data and the development of highly sophisticated computational methods is highlighted. With the cesium-based diode-pumped alkali laser and remote plasma etching of Si3N4 as examples, we demonstrate how accurate and comprehensive datasets for electron collisions enable complex modeling of plasma-using technologies that empower our high-technology-based society.

  5. IrPd nanoalloys: simulations, from surface segregation to local electronic properties

    Energy Technology Data Exchange (ETDEWEB)

    Andriamiharintsoa, T. H. [Institut de Physique et Chimie des Matériaux de Strasbourg CNRS-UDS UMR 7504 (France); Rakotomahevitra, A. [Institut pour la Maîtrise de l’Énergie, Faculté des sciences d’Antananarivo (Madagascar); Piccolo, L. [Institut de Recherches sur la Catalyse et l’Environnement de Lyon IRCELYON, UMR 5256 CNRS and Université Lyon 1 (France); Goyhenex, C., E-mail: christine.goyhenex@ipcms.unistra.fr [Institut de Physique et Chimie des Matériaux de Strasbourg CNRS-UDS UMR 7504 (France)

    2015-05-15

    Using semi-empirical modeling, namely tight-binding at different levels of accuracy, the chemical, crystallographic, and electronic structures of bimetallic IrPd nanoparticles are characterized. For the purpose, model cuboctahedral particles containing 561 atoms are considered. Atomistic simulations show that core–shell nanoparticles are highly stable, with a strong surface segregation of Pd, at least for one atomic shell thickness. Within self-consistent tight-binding calculations founded on the density functional theory, an accurate insight is given into the electronic structure of these materials which have a high potential as catalysts.

  6. Surface magnetism Correlation of structural, electronic and chemical properties with magnetic behavior

    CERN Document Server

    Getzlaff, Mathias

    2010-01-01

    This volume reviews on selected aspects related to surface magnetism, a field of extraordinary interest during the last decade. The special emphasis is set to the correlation of structural, electronic and magnetic properties in rare earth metal systems and ferromagnetic transition metals. This is made possible by the combination of electron emission techniques (spin polarized photoelectron spectroscopy, magnetic dichroism in photoemission and spin polarized metastable deexcitation spectroscopy) and local probes with high lateral resolution down to the atomic scale (spin polarized scanning tunneling microscopy / spectroscopy).

  7. Bulk and surface electromagnetic response of metallic metamaterials to convection electrons

    Science.gov (United States)

    So, Jin-Kyu; Jang, Kyu-Ha; Park, Gun-Sik; Garcia-Vidal, F. J.

    2011-08-01

    The electromagnetic response of three-dimensional metallic metamaterials with isotropic effective index of refraction to fast-moving electrons is studied by numerical simulations. The considered metamaterials can support Cerenkov radiation [P. A. Cherenkov, Dokl. Akad. Nauk SSSR 2, 451 (1934)], and their effective dielectric behavior is confirmed by the detailed angular dependence of the generated radiation cone on the kinetic energy of electrons. Moreover, in addition to the predicted bulk modes, surface electromagnetic excitation is observed in a specific type of metamaterials and its dispersion is sensitive to the thickness of the subwavelength rods.

  8. Non-vacuum electron-beam carburizing and surface hardening of mild steel

    Energy Technology Data Exchange (ETDEWEB)

    Bataev, I.A., E-mail: ivanbataev@ngs.ru [Novosibirsk State Technical University, K. Marks 20, 630092 Novosibirsk (Russian Federation); Golkovskii, M.G., E-mail: M.G.Golkovski@inp.nsk.su [Budker Institute of Nuclear Physics SB RAS, Lavrentieva Prospect 11, 630090 Novosibirsk (Russian Federation); Losinskaya, A.A., E-mail: anna.losinskaya@mail.ru [Novosibirsk State Technical University, K. Marks 20, 630092 Novosibirsk (Russian Federation); Bataev, A.A., E-mail: bataev@adm.nstu.ru [Novosibirsk State Technical University, K. Marks 20, 630092 Novosibirsk (Russian Federation); Popelyukh, A.I., E-mail: aip13@mail.ru [Novosibirsk State Technical University, K. Marks 20, 630092 Novosibirsk (Russian Federation); Hassel, T., E-mail: hassel@iw.uni-hannover.de [Leibniz University, Welfengarten 1, 30167 Hannover (Germany); Golovin, D.D., E-mail: ddgolovin@yandex.ru [Novosibirsk State Technical University, K. Marks 20, 630092 Novosibirsk (Russian Federation)

    2014-12-15

    Highlights: • Steel specimens were carburized by non-vacuum electron-beam cladding. • The depth of the clad layers reached 2.6 mm. • The cladding rate was 1.8 m{sup 2}/h, the quenching rate 12.6 m{sup 2}/h. • The microhardness of the quenched and tempered layers reached 8 GPa. - Abstract: In this paper, we study the structure, microhardness, and tribological properties of surface layers of mild (0.19% C) steel, which was formed by electron-beam cladding with an iron–graphite powder mixture followed by quenching and tempering. A 1.4 MeV electron beam that was extracted into air was used. Cladding of steel with the iron–graphite mixture at a beam current of 24 and 26 mA formed a hypoeutectic cast iron layer (2.19% C) and a hypereutectoid steel (1.57% C) layer, which were 2.0 and 2.6 mm thick, respectively. The microhardness of the surface-quenched and tempered steel and cast iron layers was 7 and 8 GPa, respectively. Electron-beam quenching of the surface layers of hypoeutectic cast iron was accompanied with multiple cracking. During the quenching of the 1.57% C steel layer, crack formation was not observed. In friction tests against fixed and loose abrasive particles, the surface layers of hypereutectoid steel and hypoeutectic cast iron that were produced by electron-beam cladding and quenching had lower wear rates than mild steel after pack carburizing, quenching, and tempering. In the sliding wear tests, the cast iron clad layer, which was subjected to electron-beam quenching and tempering, exhibited the highest wear resistance. Electron-beam treatment can be used to harden local areas of large workpieces. It is reasonable to treat clad layers of high-carbon steel with electron-beam quenching and tempering. To prevent multiple cracking, white cast iron layers should not be quenched.

  9. Dental enamel: qualitative evaluation of the surface after application of aluminum oxide (microetching using the scanning electron microscope

    Directory of Open Access Journals (Sweden)

    SILVA Paulo César Gomes

    2000-01-01

    Full Text Available Dentistry nowadays can count on a wide range of resources to treat patients. With the development of adhesive materials and several newly introduced restorative techniques, the dental structure can be subjected to different sorts of surface treatment. The use of aluminum oxide flow at high speed to remove dental structure was described by Black in 1945, however, the literature regarding the use of aluminum oxide jet is still scarce, as far as the alterations occurring in the dental structure are concerned. At the present, with the development of new abrasive air equipment, microabrasion has been added to several adhesive restorative techniques, in the preparation of the dental surface and of inner surfaces of indirect restorations, which will receive the application of adhesive materials. The aim of this study was to assess the alterations produced by abrasive air applied on the dental enamel by means of electronic microscopy, taking into consideration micromorphological surface alterations. The importance of this study is based on the fact that alternative surface treatments both chemical and mechanical could be introduced in surface priming, including dental enamel priming.

  10. First-principle studies on the electronic structure of Fe3O4(110) surface

    Institute of Scientific and Technical Information of China (English)

    LI Yan-li; YAO Kai-lun; LIU Zu-li

    2007-01-01

    The first-principle was employed to study the six possible models for the Fe3O4(110) surface, namely the AB-terminated surface (AB model), the AB-terminated with Fen vacancy (AB-FeA vac model), the AB-terminated with FeB vacancy (AB-FeB vac model), the B-terminated surface (B model), the B-terminated surface with FeB vacancy (B-FeB vac model) and the B-terminated surface with O vacancy (B-O vac model). The stability, the electronic structure and the magnetic properties of the six surface models were also calculated. The results predict that the B-O vac model is more stable than other types of surface models. The half-metallic property remain in the AB and B models, while the other four surface models exhibit metallic properties. At the same time, the AB, AB-FeAvac, AB-FeB vac, B and the B-FeB vac models have ferrimagnetic properties, while the B-O vac model has antiferromagnetic property.

  11. Patterned surface with controllable wettability for inkjet printing of flexible printed electronics.

    Science.gov (United States)

    Nguyen, Phuong Q M; Yeo, Lip-Pin; Lok, Boon-Keng; Lam, Yee-Cheong

    2014-03-26

    Appropriate control of substrate surface properties prior to inkjet printing could be employed to improve the printing quality of fine resolution structures. In this paper, novel methods to fabricate patterned surfaces with a combination of hydrophilic and hydrophobic properties are investigated. The results of inkjet printing of PEDOT/PSS conductive ink on these modified surfaces are presented. Selective wetting was achieved via a two-step hydrophilic-hydrophobic coating of 3-aminopropyl trimethoxysilane (APTMS) and 3M electronic grade chemical respectively on PET surfaces; this was followed by a selective hydrophilic treatment (either atmospheric O2/Ar plasma or UV/ozone surface treatment) with the aid of a Nickel stencil. Hydrophobic regions with water contact angle (WCA) of 105° and superhydrophilic regions with WCA <5° can be achieved on a single surface. During inkjet printing of the treated surfaces, PEDOT/PSS ink spread spontaneously along the hydrophilic areas while avoiding the hydrophobic regions. Fine features smaller than the inkjet droplet size (approximately 55 μm in diameter) can be successfully printed on the patterned surface with high wettability contrast.

  12. Surface chemistry and electronic structure of nonpolar and polar GaN films

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, Monu; Krishna, T.C. Shibin; Aggarwal, Neha; Gupta, Govind, E-mail: govind@nplindia.org

    2015-08-01

    Highlights: • Surface chemistry and electronic structure of polar and nonpolar GaN is reported. • Influence of polarization on electron affinity of p & np GaN films is investigated. • Correlation between surface morphology and polarity has been deduced. - Abstract: Photoemission and microscopic analysis of nonpolar (a-GaN/r-Sapphire) and polar (c-GaN/c-Sapphire) epitaxial gallium nitride (GaN) films grown via RF-Molecular Beam Epitaxy is reported. The effect of polarization on surface properties like surface states, electronic structure, chemical bonding and morphology has been investigated and correlated. It was observed that polarization lead to shifts in core level (CL) as well as valence band (VB) spectra. Angle dependent X-ray Photoelectron Spectroscopic analysis revealed higher surface oxide in polar GaN film compared to nonpolar GaN film. On varying the take off angle (TOA) from 0° to 60°, the Ga−O/Ga−N ratio varied from 0.11–0.23 for nonpolar and 0.17–0.36 for polar GaN film. The nonpolar film exhibited N-face polarity while Ga-face polarity was perceived in polar GaN film due to the inherent polarization effect. Polarization charge compensated surface states were observed on the polar GaN film and resulted in downward band bending. Ultraviolet photoelectron spectroscopic measurements revealed electron affinity and ionization energy of 3.4 ± 0.1 eV and 6.8 ± 0.1 eV for nonpolar GaN film and 3.8 ± 0.1 eV and 7.2 ± 0.1 eV for polar GaN film respectively. Field Emission Scanning Electron Microscopy measurements divulged smooth morphology with pits on polar GaN film. The nonpolar film on the other hand showed pyramidal structures having facets all over the surface.

  13. Two dimensional electron gas confined over a spherical surface: Magnetic moment

    Energy Technology Data Exchange (ETDEWEB)

    Hernando, A; Crespo, P [Instituto de Magnetismo Aplicado, UCM-CSIC-ADIF, Las Rozas. P. O. Box 155, Madrid 28230 (Spain) and Dpto. Fisica de Materiales, Universidad Complutense (Spain); Garcia, M A, E-mail: antonio.hernando@adif.es [Instituto de Ceramica y Vidrio, CSIC c/Kelsen, 5 Madrid 28049 (Spain)

    2011-04-01

    Magnetism of capped nanoparticles, NPs, of non-magnetic substances as Au and ZnO is briefly reviewed. The source of the magnetization is discussed on the light of recent X-ray magnetic circular dichroism experiments. As magnetic dichroism analysis has pointed out impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. It is proposed that mesoscopic collective orbital magnetic moments induced at the surface states can account for the experimental magnetism characteristic of these nanoparticles. The total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 10{sup 2} or 10{sup 3} Bohr magnetons.

  14. Electron microscopic time-lapse visualization of surface pore filtration on particulate matter trapping process.

    Science.gov (United States)

    Sanui, Ryoko; Hanamura, Katsunori

    2016-09-01

    A scanning electron microscope (SEM) was used to dynamically visualize the particulate matter (PM) trapping process on diesel particulate filter (DPF) walls at a micro scale as 'time-lapse' images corresponding to the increase in pressure drop simultaneously measured through the DPF. This visualization and pressure drop measurement led to the conclusion that the PM trapping in surface pores was driven by PM bridging and stacking at constricted areas in porous channels. This caused a drastic increase in the pressure drop during PM accumulation at the beginning of the PM trapping process. The relationship between the porous structure of the DPF and the depth of the surface pore was investigated in terms of the porosity distribution and PM penetration depth near the wall surface with respect to depth. The pressure drop calculated with an assumed surface pore depth showed a good correspondence to the measured pressure drop.

  15. Semiconducting electronic property of graphene adsorbed on (0001) surfaces of SiO2.

    Science.gov (United States)

    Nguyen, Thanh Cuong; Otani, Minoru; Okada, Susumu

    2011-03-11

    First-principles total energy calculations are performed to investigate the energetics and electronic structures of graphene adsorbed on both an oxygen-terminated SiO2 (0001) surface and a fully hydroxylated SiO2 (0001) surface. We find that there are several stable adsorption sites for graphene on both O-terminated and hydroxylated SiO2 surfaces. The binding energy in the most stable geometry is found to be 15 meV per C atom, indicating a weak interaction between graphene and SiO2 (0001) surfaces. We also find that the graphene adsorbed on SiO2 is a semiconductor irrespective of the adsorption arrangement due to the variation of on-site energy induced by the SiO2 substrate.

  16. Electron spectroscopic study of electronic and morphological modifications of the WSe{sub 2} surface induced by Rb adsorption

    Energy Technology Data Exchange (ETDEWEB)

    Buck, Jens

    2010-07-20

    The rubidium-covered surface of the semiconducting transition metal dichalcogenide tungsten diselenide (WSe{sub 2}) is examined using photoelectron spectroscopy (PES) and photoemission electron microscopy (PEEM). Adsorbed Rb is known to induce a variety of effects in this system concerning electronic, structural, and mechanical properties. In this work, the surface potential created by charge transfer upon Rb deposition is examined in thermal equilibrium (band bending) and stationary non-equilibrium (surface photovoltage (SPV) effect), which is induced by the absorption of light. It is shown that combined measurements and numerical simulations of the SPV effect as a function of the photon flux can be exploited for the estimation of many material parameters of the system, especially of the unoccupied adsorbate state. Issues of extending a conventional photoelectron spectrometer setup by a secondary light source will be discussed in the context of simulations and calibration measurements. The customization of an existing theoretical model of the SPV effect for the WSe{sub 2}: Rb system is introduced, and a comprehensive validation of the obtained predictions is given in the context of experimental data. In addition, the self-organized formation of Rb domains at room temperature was examined by application of spatially resolved XPS spectroscopy using the PEEM setup at the end station of beamline UE49/PGMa at the BESSY II synchrotron facility. From the obtained results, the arrangement of Rb in surface lattices can be concluded. Furthermore, an X-Ray absorption study of self-organized nanostructure networks, aiming at the chemical characterization, is presented. Based on the interpretation of the examined structures as tension-induced cracks, a statistical approach to analyzing large-scale features was pursued. First accordance with the predictions made by a primitive, mechanical model of crack creation developed here gives gives some evidence for the validity of the

  17. A Note on the Relationship Between Temperature and Water Vapor over Oceans, Including Sea Surface Temperature Effects

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    An ideal and simple formulation is successfully derived that well represents a quasi-linear relationship found between the domain-averaged water vapor, Q (mm), and temperature, T (K), fields for the three tropical oceans (i.e., the Pacific, Atlantic and Indian Oceans) based on eleven GEOS-3 [Goddard Earth Observing System (EOS) Version-3] global re-analysis monthly products. A Q - T distribution analysis is also performed for the tropical and extra-tropical regions based on in-situ sounding data and numerical simulations [GEOS-3 and the Goddard Cumulus Ensemble (GCE) model]. A similar positively correlated Q - T distribution is found over the entire oceanic and tropical regions; however, Q increases faster with T for the former region. It is suspected that the tropical oceans may possess a moister boundary layer than the Tropics. The oceanic regime falls within the lower bound of the tropical regime embedded in a global, curvilinear Q - T relationship. A positive correlation is also found between T and sea surface temperature (SST); however, for one degree of increase in T, SST is found to increase 1.1 degrees for a warmer ocean, which is slightly less than an increase of 1.25 degrees for a colder ocean. This seemingly indicates that more (less) heat is needed for an open ocean to maintain an air mass above it with a same degree of temperature rise during a colder (warmer) season [or in a colder (warmer) region]. Q and SST are also found to be positively correlated. Relative humidity (RH) exhibits similar behaviors for oceanic and tropical regions. RH increases with increasing SST and T over oceans, while it increases with increasing T in the Tropics. RH, however, decreases with increasing temperature in the extratropics. It is suspected that the tropical and oceanic regions may possess a moister local boundary layer than the extratropics so that a faster moisture increase than a saturated moisture increase is favored for the former regions.T, Q, saturated water

  18. Surface photochemistry: Diffuse reflectance studies of thioketones included into p-tert-butylcalix[6 and 8]arenes

    Science.gov (United States)

    Vieira Ferreira, L. F.; Ferreira Machado, I.; Oliveira, A. S.; Da Silva, J. P.; Krawczyk, A.; Sikorski, M.

    2007-02-01

    This paper presents time resolved laser induced luminescence (LIL) and diffuse reflectance laser flash-photolysis (DRLFP) studies of solid powdered samples of xanthione (XT) and 4H-1-benzopyran-4-thione (BPT). These thioketones form inclusion complexes with p-tert-butylcalix[6]arene (CLX[6]) and p-tert-butylcalix[8]arene (CLX[8]). Room temperature air equilibrated LIL studies for XT/CLX[8] inclusion complex have shown the existence of both fluorescence and delayed fluorescence emission (S 2 → S 0 emissions in the nanosecond and microsecond time ranges, respectively) peaking at ca. 460 nm while phosphorescence peaks at about 670 nm with a half life of about 4 μs. For the BPT/CLX[8] inclusion complex, the emissions now peak at ca. 450 and 630 nm, respectively. When these two thioketones are included into the CLX[6] nanocavities similar luminescence spectra were detected. The phosphorescence spectra in all cases present a clear vibrational structure characteristic of non-polar environments, in accordance with the non-polar character of the calixarene's cavities. Diffuse reflectance transient absorption spectra revealed in all cases the presence of the triplet state of the thioketones and also of longer lived species. The use of chromatographic methods (GC-MS) allowed us to identify the formation of xanthone, chromone and hydroxy-thioketones following laser irradiation at 355 or 337 nm.

  19. Vibrational Spectra and Potential Energy Surface for Electronic Ground State of Jet-Cooled Molecule S2O

    Institute of Scientific and Technical Information of China (English)

    WANG Xiao-Yan; DING Shi-Liang

    2004-01-01

    The vibration states of transition molecule S2O, including both bending and stretching vibrations, are studied in the framework of dynamical symmetry groups U1(4) U2(4). We get all the vibration spectra of S2O by fitting 22 spectra data with 10 parameters. The fitting rms of the Hamiltonian is 2.12 cm-1. With the parameters and Lie algebraic theory, we give the analytical expression of the potential energy surface, which helps us to calculate the dissociation energy and force constants of S2O in the electronic ground state.

  20. Rapid electron exchange between surface-exposed bacterial cytochromes and Fe(III) minerals

    Energy Technology Data Exchange (ETDEWEB)

    White, Gaye F.; Shi, Zhi; Shi, Liang; Wang, Zheming; Dohnalkova, Alice; Marshall, Matthew J.; Fredrickson, Jim K.; Zachara, John M.; Butt, Julea N.; Richardson, David; Clarke, Thomas A.

    2013-04-16

    The mineral respiring bacterium Shewanella oneidensis uses a protein complex, MtrCAB, composed of two decaheme cytochromes brought together inside a transmembrane porin to transport electrons across the outer membrane to a variety of mineral-based electron acceptors. A proteoliposome system that contains methyl viologen as an internalised electron carrier has been used to investigate how the topology of the MtrCAB complex relates to its ability to transport electrons across a lipid bilayer to externally-located Fe(III) oxides. With MtrA facing the interior and MtrC exposed on the outer surface of the phospholipid bilayer, direct electron transfer from the interior through MtrCAB to solid-phase Fe(III) oxides was demonstrated. The observed rates of conduction through the protein complex were 2 to 3 orders of magnitude higher than that observed in whole cells, demonstrating that direct electron exchange between MtrCAB and Fe(III) oxides is efficient enough to support in-vivo, anaerobic, solid phase iron respiration.

  1. Electronic Wiring of a Multi-Redox Site Membrane Protein in a Biomimetic Surface Architecture

    Science.gov (United States)

    Friedrich, Marcel G.; Robertson, Joseph W. F.; Walz, Dieter; Knoll, Wolfgang; Naumann, Renate L. C.

    2008-01-01

    Bioelectronic coupling of multi-redox-site membrane proteins was accomplished with cytochrome c oxidase (CcO) as an example. A biomimetic membrane system was used for the oriented immobilization of the CcO oxidase on a metal electrode. When the protein is immobilized with the CcO binding side directed toward the electrode and reconstituted in situ into a lipid bilayer, it is addressable by direct electron transfer to the redox centers. Electron transfer to the enzyme via the spacer, referred to as electronic wiring, shows an exceptionally high rate constant. This allows a kinetic analysis of all four consecutive electron transfer steps within the enzyme to be carried out. Electron transfer followed by rapid scan cyclic voltametry in combination with surface-enhanced resonance Raman spectroscopy provides mechanistic and structural information about the heme centers. Probing the enzyme under turnover conditions showed mechanistic insights into proton translocation coupled to electron transfer. This bioelectronic approach opens a new field of activity to investigate complex processes in a wide variety of membrane proteins. PMID:18222995

  2. Scanning probe microscopy investigation of self-organized perylenetetracarboxdiimide nanostructures at surfaces: structural and electronic properties.

    Science.gov (United States)

    Palermo, Vincenzo; Liscio, Andrea; Gentilini, Desirée; Nolde, Fabian; Müllen, Klaus; Samorì, Paolo

    2007-01-01

    A scanning probe microscopy investigation of the self-organization and local electronic properties of spin-coated ultrathin films of N-alkyl substituted perylenetetracarboxdiimide (PDI) is described. By carefully balancing the interplay between molecule-molecule and molecule-substrate interactions, PDI is able to form highly ordered supramolecular architectures on flat surfaces from solution. On an electrically insulating yet highly polar surface (mica) PDI forms strongly anisotropic architectures with needlelike structures with lengths of up to a few micrometers. On a conductive yet apolar surface (highly oriented pyrolytic graphite), the competition between the strong molecule-substrate interactions and the intermolecular forces leads to the generation of more disordered structures. The local electronic properties of these architectures are studied by Kelvin probe force microscopy by estimating their surface potential (SP). Quantitative measurements of the SP are obtained by analyzing the experimentally estimated SP data with a computational model, which discriminates between the intrinsic SP and the effect of long-range tip-surface interactions. The SP of PDI aggregates depends on the structural order at the supramolecular level. Narrow needles of constant width reveal identical SPs independent of length. Wider needles with a polydisperse width distribution exhibit a greater SP.

  3. Surface Modification of Light Alloys by Low-Energy High-Current Pulsed Electron Beam

    Directory of Open Access Journals (Sweden)

    X. D. Zhang

    2012-01-01

    Full Text Available This paper reviews results obtained by the research groups developing the low-energy high-current pulsed electron beam (LEHCPEB in Dalian (China and Metz (France on the surface treatment of light alloys. The pulsed electron irradiation induces an ultra-fast thermal cycle at the surface combined with the formation of thermal stress and shock waves. As illustrated for Mg alloys and Ti, this results in deep subsurface hardening (over several 100 μm which improves the wear resistance. The analysis of the top surface melted surface of light alloys also often witnesses evaporation and condensation of chemical species. This phenomenon can significantly modify the melt chemistry and was also suggested to lead to the development of specific solidification textures in the rapidly solidified layer. The potential use of the LEHCPEB technique for producing thermomechanical treatments under the so-called heating mode and, thus, modify the surface crystallographic texture, and enhance solid-state diffusion is also demonstrated in the case of the FeAl intermetallic compound.

  4. Real-space Mapping of Surface Trap States in CIGSe Nanocrystals using 4D Electron Microscopy

    KAUST Repository

    Bose, Riya

    2016-05-26

    Surface trap states in semiconductor copper indium gallium selenide nanocrystals (NCs) which serve as undesirable channels for non-radiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with sub-picosecond temporal and nanometer spatial resolutions. Here, we precisely map the surface charge carrier dynamics of copper indium gallium selenide NCs before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs.

  5. Hydrogen effect on zirconium alloy surface treated by pulsed electron beam

    Energy Technology Data Exchange (ETDEWEB)

    Pushilina, N.S.; Lider, A.M. [Department of General Physics, Institute of Physics and Technology, National Research Tomsk Polytechnic University, Lenin Avenue 30, Tomsk 634050 (Russian Federation); Kudiiarov, V.N., E-mail: viktor.kudiiarov@gmail.com [Department of General Physics, Institute of Physics and Technology, National Research Tomsk Polytechnic University, Lenin Avenue 30, Tomsk 634050 (Russian Federation); Chernov, I.P. [Department of General Physics, Institute of Physics and Technology, National Research Tomsk Polytechnic University, Lenin Avenue 30, Tomsk 634050 (Russian Federation); Ivanova, S.V. [National Research Nuclear University “MIFI”, Kashirskoye shosse 31, Moscow 115409 (Russian Federation)

    2015-01-15

    Influence of modification by pulsed electron beam (PEB) and hydrogen adsorption in zirconium alloys have been investigated. Treatment of Zr–1Nb alloy by high-current PEB allows for a decrease in the amount of hydrogen absorbed by the samples during the hydrogenation process from gas atmosphere in the temperature range of (350–550 °S). The effect of the PEB surface treatment on the hydrogen adsorption connected with the formation of a protective oxide film after PEB irradiation and also by the formation of a specific hardening structure under the action of irradiation at temperatures exceeding the melting temperature from the subsequent high-speed surface cooling.

  6. Electronic detection of surface plasmon polaritons by metal-oxide-silicon capacitor

    Directory of Open Access Journals (Sweden)

    Robert E. Peale

    2016-09-01

    Full Text Available An electronic detector of surface plasmon polaritons (SPPs is reported. SPPs optically excited on a metal surface using a prism coupler are detected by using a close-coupled metal-oxide-silicon (MOS capacitor. Incidence-angle dependence is explained by Fresnel transmittance calculations, which also are used to investigate the dependence of photo-response on structure dimensions. Electrodynamic simulations agree with theory and experiment and additionally provide spatial intensity distributions on and off the SPP excitation resonance. Experimental dependence of the photoresponse on substrate carrier type, carrier concentration, and back-contact biasing is qualitatively explained by simple theory of MOS capacitors.

  7. Electronic detection of surface plasmon polaritons by metal-oxide-silicon capacitor

    Science.gov (United States)

    Peale, Robert E.; Smith, Evan; Smith, Christian W.; Khalilzadeh-Rezaie, Farnood; Ishigami, Masa; Nader, Nima; Vangala, Shiva; Cleary, Justin W.

    2016-09-01

    An electronic detector of surface plasmon polaritons (SPPs) is reported. SPPs optically excited on a metal surface using a prism coupler are detected by using a close-coupled metal-oxide-silicon (MOS) capacitor. Incidence-angle dependence is explained by Fresnel transmittance calculations, which also are used to investigate the dependence of photo-response on structure dimensions. Electrodynamic simulations agree with theory and experiment and additionally provide spatial intensity distributions on and off the SPP excitation resonance. Experimental dependence of the photoresponse on substrate carrier type, carrier concentration, and back-contact biasing is qualitatively explained by simple theory of MOS capacitors.

  8. Cherenkov terahertz surface plasmon excitation by an electron beam over an ultrathin metal film

    Science.gov (United States)

    Kumar, Pawan; Kumar, Rajeev; Rajouria, Satish Kumar

    2016-12-01

    The mechanism of Cherenkov excitation of terahertz (THz) surface plasma wave (SPW), by a relativistic electron beam propagating over an ultrathin metal film deposited on glass, is investigated. The SPW field falls off exponentially in vacuum as well as glass, while the surface plasmon resonant frequency is lowered by the reduction of film thickness. The SPW field causes density bunching of the beam leading to current modulation and generation of THz radiation via the Cherenkov interaction. The frequency of the THz decreases with the energy of the beam, whereas the growth rate increases.

  9. Isocyanide ligands adsorbed on metal surfaces: applications in catalysis, nanochemistry, and molecular electronics.

    Science.gov (United States)

    Angelici, Robert J; Lazar, Mihaela

    2008-10-20

    Knowledge of the coordination chemistry and reactivity of isocyanide ligands in transition-metal complexes forms the basis for understanding the adsorption and reactions of isocyanides on metal surfaces. In this overview, we explore reactions (often catalytic) of isocyanides adsorbed on metal surfaces that reflect their patterns of reactivity in metal complexes. We also examine applications of isocyanide adsorption to the stabilization of metal nanoparticles, the functionalization of metal electrodes, and the creation of conducting organic-metal junctions in molecule-scale electronic devices.

  10. Effect of ion and electron beam irradiation on surface morphology and optical properties of PVA

    Institute of Scientific and Technical Information of China (English)

    HM Eyssa; MO sman; SAK andil; MMA bdelrahman

    2015-01-01

    Polyvinyl alcohol (PVA) is a well-known friendly polymer for paper-making, textiles, and a variety of coat-ings, biomedical applications such as artificial pancreas, synthetic vitreous body, wound dressing, artificial skin, and cardiovascular device. In this paper, ion/electron beam is employed to get insight into the irradiation effect on surface morphology and optical properties of PVA polymer. UV-Vis spectra are recorded to investigate the effect of induced defects on the optical band gap and the formed carbon clusters size. Scanning electron microscopy (SEM) is used to relate and investigate surface morphology and optical properties of the target poly-mer with different doses (15, 30 and 60 min). Also, PVA polymer is subjected to theoretical studies by using semi-empirical PM7 quantum chemical method.

  11. Surface modification of Ti alloy by electro-explosive alloying and electron-beam treatment

    Energy Technology Data Exchange (ETDEWEB)

    Gromov, Victor, E-mail: gromov@physics.sibsiu.ru; Kobzareva, Tatiana, E-mail: kobzarevatanya@mail.ru; Budovskikh, Evgeniy, E-mail: budovskih-ea@physics.sibsiu.ru; Baschenko, Lyudmila, E-mail: gromov@physics.sibsiu.ru [Siberian State Industrial University, 42, Kirov Str., Novokuznetsk, 654007 (Russian Federation); Ivanov, Yuryi, E-mail: yufi55@mail.ru [Institute of High Current Electronics SB RAS, 4, Akademicheskii Av. Tomsk, 634055 (Russian Federation); National Research Tomsk State University, 30, Lenina Av. Tomsk, 634034 (Russian Federation)

    2016-01-15

    By methods of modern physical metallurgy the analysis of structure phase states of titanium alloy VT6 is carried out after electric explosion alloying with boron carbide and subsequent irradiation by pulsed electron beam. The formation of an electro-explosive alloying zone of a thickness up to 50 µm, having a gradient structure, characterized by decrease in the concentration of carbon and boron with increasing distance to the treatable surface has been revealed. Subsequent electron-beam treatment of alloying zone leads to smoothing of the alloying area surface and is accompanied by the multilayer structure formation at the depth of 30 µm with alternating layers with different alloying degrees having the structure of submicro - and nanoscale level.

  12. Surface modification of Ti alloy by electro-explosive alloying and electron-beam treatment

    Science.gov (United States)

    Gromov, Victor; Kobzareva, Tatiana; Ivanov, Yuryi; Budovskikh, Evgeniy; Baschenko, Lyudmila

    2016-01-01

    By methods of modern physical metallurgy the analysis of structure phase states of titanium alloy VT6 is carried out after electric explosion alloying with boron carbide and subsequent irradiation by pulsed electron beam. The formation of an electro-explosive alloying zone of a thickness up to 50 µm, having a gradient structure, characterized by decrease in the concentration of carbon and boron with increasing distance to the treatable surface has been revealed. Subsequent electron-beam treatment of alloying zone leads to smoothing of the alloying area surface and is accompanied by the multilayer structure formation at the depth of 30 µm with alternating layers with different alloying degrees having the structure of submicro - and nanoscale level.

  13. Influence of surface roughness on field emission of electrons from carbon nanotube films.

    Science.gov (United States)

    Liu, Huarong; Saito, Yahachi

    2010-06-01

    Electron field emission properties of a nanotube film are influenced not only by a field enhancement factor of carbon nanotubes (CNTs) beta(CNT) but also by that of film morphology beta(P). A simple method to separate beta(P), and beta(CNT) is proposed by using their different dependences on the cathode-anode distance. Analyses conducted for CNT emitters with rough surface exhibit that beta(P) ranges from 1 to approximately 4.5. The separated beta(CNT) values are in good agreement with the CNT geometries observed by a scanning electron microscope. Variation in beta(P)-values is ascribed to the surface roughness of the CNT films.

  14. Electronic structure and chemical reaction of Ca deposition on regioregular poly(3-hexylthiophene) surfaces

    Institute of Scientific and Technical Information of China (English)

    ZHAO Wei; GUO YuXian; FENG XueFei; ZHANG Liang; ZHANG WenHua; ZHU JunFa

    2009-01-01

    Conjugated polymer, regioregular poly(3-hexylthiophene) (rr-P3HT), films were prepared by spin-coating the rr-P3HT chloroform solution onto clean silicon wafer surfaces. The chemical re-action and electronic structure of Ca deposition on rr-P3HT surfaces were in situ investigated by synchrotron radiation photoemission spectroscopy (SRPES) and X-ray photoemission spectros-copy (XPS). Upon Ca deposition, Ca-induced band bending of rr-P3HT is observed. In addition, Ca atoms preferentially react with S atoms of rr-P3HT. No obvious reaction between Ca and C atoms can be found. Through the investigation of the evolution of valence band spectra and secondary electron cut-off of rr-P3HT during the process of Ca deposition, an energy level alignment diagram at the Ca/rr-P3HT interface is derived.

  15. Graphene oxide-facilitated electron transfer of metalloproteins at electrode surfaces.

    Science.gov (United States)

    Zuo, Xiaolei; He, Shijiang; Li, Di; Peng, Cheng; Huang, Qing; Song, Shiping; Fan, Chunhai

    2010-02-02

    Graphene is a particularly useful nanomaterial that has shown great promise in nanoelectronics. Because of the ultrahigh electron mobility of graphene and its unique surface properties such as one-atom thickness and irreversible protein adsorption at surfaces, graphene-based materials might serve as an ideal platform for accommodating proteins and facilitating protein electron transfer. In this work, we demonstrate that graphene oxide (GO) supports the efficient electrical wiring the redox centers of several heme-containing metalloproteins (cytochrome c, myoglobin, and horseradish peroxidase) to the electrode. Importantly, proteins retain their structural intactness and biological activity upon forming mixtures with GO. These important features imply the promising applications of GO/protein complexes in the development of biosensors and biofuel cells.

  16. Electronic structure modification of the KTaO3 single-crystal surface by Ar+ bombardment

    Science.gov (United States)

    Wadehra, Neha; Tomar, Ruchi; Halder, Soumyadip; Sharma, Minaxi; Singh, Inderjit; Jena, Nityasagar; Prakash, Bhanu; De Sarkar, Abir; Bera, Chandan; Venkatesan, Ananth; Chakraverty, S.

    2017-09-01

    Oxygen vacancies play an important role in controlling the physical properties of a perovskite oxide. We report alterations in the electronic properties of a cubic perovskite oxide, namely, KTaO3, as a function of oxygen vacancies. The conducting surface of the KTaO3 single-crystal substrate has been realized via Ar+ irradiation. The band gap changes as a function of conductivity which is controlled by irradiation time, indicating the formation of defect states. Kelvin probe force microscopy suggests a sharp increase in the work function upon Ar+ irradiation for a short period of time followed by a monotonic decrease, as we increase the irradiation time. Our experimental findings along with theoretical simulations suggest a significant surface dipole contribution and an unusual change in the electronic band line-up of KTaO3 due to oxygen vacancies.

  17. Effect of strain on geometric and electronic structures of graphene on a Ru(0001) surface

    Institute of Scientific and Technical Information of China (English)

    Sun Jia-Tao; Du Shi-Xuan; Xiao Wen-De; Hu Hao; Zhang Yu-Yang; Li Guo; Gao Hong-Jun

    2009-01-01

    The atomic and electronic structures of a graphene monolayer on a Ru(0001) surface under compressive strain are investigated by using first-principles calculations. Three models of graphene monolayers with different carbon periodicities due to the lattice mismatch are proposed in the presence and the. absence of the Ru(0001) substrate separately. Considering the strain induced by the lattice mismatch, we optimize the atomic structures and investigate the electronic properties of the graphene. Our calculation results show that the graphene layers turn into periodic corrugations and there exist strong chemical bonds in the interface between the graphene N x N superlattice and the substrate. The strain does not induce significant changes in electronic structure. Furthermore, the results calculated in the local density approximation (LDA) are compared with those obtained in the generalized gradient approximation (GGA), showing that the LDA results are more reasonable than the GGA results when only two substrate layers are used in calculation.

  18. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Wang, R.; Williams, C. C., E-mail: clayton@physics.utah.edu [Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112 (United States)

    2015-09-15

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  19. Surface morphology of the endolymphatic duct in the rat. A scanning electron microscopy study

    DEFF Research Database (Denmark)

    Qvortrup, K; Rostgaard, Jørgen; Bretlau, P

    1995-01-01

    Following intracardiac vascular perfusion fixation of 8 rats with glutaraldehyde in a buffered and oxygenated blood substitute, the vestibular aqueduct and endolymphatic duct were opened by microsurgery of the resulting 16 temporal bones. Optimum preservation of the epithelium for scanning electron...... were identified with the scanning electron microscope. A polygonal and oblong epithelial cell was observed in the largest number throughout the duct, and in the juxtasaccular half of the duct, two additional types of epithelial cells were observed. The scanning electron microscopic observations...... microscopy was attained by coating of the specimens with osmium tetroxide and thiocarbohydrazide followed by a continuous dehydration procedure. This technique permitted, for the first time, an investigation of the surface morphology of the epithelial cells in the endolymphatic duct. Three types of cells...

  20. Ultra structural studies of the surface of Hymenolepis nana by scanning and transmission electron microscopy.

    Science.gov (United States)

    Abouzakham, A A; Romia, S A; Hegazi, M M

    1990-06-01

    Scanning electron microscopy of the surface of Hymenolepis nana indicated that dense populations of microtriches occur on scolex proper, suckers and strobila, with an average density of 20/micron2. The excellent preservation of microtriches proves the efficacy of the critical point drying method for preparing cestodes for study of SEM. The cytological structure of the tegument of H. nana corresponds in general to that of other tapeworms.

  1. The Role of Shewanella oneidensis MR-1 Outer Surface Structures in Extracellular Electron Transfer

    Science.gov (United States)

    2010-01-01

    bacteria such as Shewanella putrefaciens sp200, Geobacter metallireducens, and G. sulfurreducens [14 – 17]. In several of these bacteria, target- ing of c...Full Paper The Role of Shewanella oneidensis MR-1 Outer Surface Structures in Extracellular Electron Transfer Rachida A. Bouhenni,a, f Gary J. Vora,b...metal reducer Shewanella oneidensis MR-1 to generate electricity in microbial fuel cells (MFCs) depends on the activity of a predicted type IV prepilin

  2. Tunable hybridization of electronic states of graphene and a metal surface

    OpenAIRE

    Gruneis, Alexander; Vyalikh, Denis

    2008-01-01

    We present an approach to monitor and control the strength of the hybridization between electronic states of graphene and metal surfaces. Inspecting the distribution of the $\\pi$ band in a high-quality graphene layer synthesized on Ni(111) by angle-resolved photoemission, we observe a new "kink" feature which indicates a strong hybridization between $\\pi$ and \\textit{d} states of graphene and nickel, respectively. Upon deposition and gradual intercalation of potassium atoms into the graphene/...

  3. Collaborative Research: Fundamental Studies of Plasma Control Using Surface Embedded Electronic Devices

    Energy Technology Data Exchange (ETDEWEB)

    Overzet, Lawrence J. [Univ. of Texas, Dallas, TX (United States); Raja, L. [Univ. of Texas, Austin, TX (United States)

    2015-06-06

    The research program was collaborative between the researchers at the University of Texas at Dallas and the University of Texas at Austin. The primary subject of this program was to investigate the possibility of active control of secondary electron emission (SEE) from surfaces in contact with plasmas and thereby actively control plasmas. Very few studies of ion-induced electron emission (IIEE) from semiconductors exist, and those that do exist primarily used high-energy ion beams in the experiments. Furthermore, those few studies took extreme measures to ensure that the measurements were performed on atomically clean surfaces because of the surface sensitivity of the IIEE process. Even a small exposure to air can change the IIEE yield significantly. In addition, much of the existing data for IIEE from semiconductors was obtained in the 1950s and ‘60s, when semiconductor materials were first being refined. As a result, nearly all of that data is for p-type Ge and Si. Before this investigation, experimental data on n-type materials was virtually non-existent. While the basic theory assumed that IIEE yields ought to be substantially independent of doping type and concentration, recent measurements of near atmospheric pressure plasmas and of breakdown suggested otherwise. These indirect measurements were made on surfaces that were not atomically clean and seemed to indicate that deep sub-surface changes to the bulk conduction band electron density could lead to substantial variations in the IIEE yield. Exactly in contradiction to the generally accepted theory. Insufficient direct data existed to settle the matter. We performed both experimental measurements and theoretical calculations of IIEE yields from both Si and Ge in order to help clarify whether or not conduction band electrons substantially change the IIEE yield. We used three wafers of each material to carry out the investigation: a heavily doped p-type, an intrinsic and a heavily doped n-type wafer. There

  4. Probing the Structure of Ionic Liquid Surfaces by Rotationally and Electronically Inelastic Scattering of no

    Science.gov (United States)

    Ziemkiewicz, M. P.; Zutz, A.; Nesbitt, D. J.

    2012-06-01

    Room temperature ionic liquids (RTIL’s) are a highly diverse class of materials with many potential technological applications. They are candidates for use in advanced electrolytes, green solvents, and supported liquid membranes for CO_2 sequestration. We present studies where inelastic scattering of high or low velocity nitric oxide provides insight into the microscopic structure of these complex surfaces. As an open shell diatomic, jet-cooled NO [^2π1/2(J = 0.5)] features both molecular and electronic collision dynamics as seen by probing scattered rotational and spin-orbit distributions respectively. These studies show substantial variation in degree of rotational and electronic excitation as ionic liquid identity is varied. Also, surface heating is found to have a strong effect on scattered spin-orbit branching, possibly due to the dependence of surface structure on temperature. This is discussed in terms of a picture where the electronic degree of freedom may serve as a sensitive measure of the cationic versus anionic nature of the top few layers of this material.

  5. A multi-scale approach to the electronic structure of doped semiconductor surfaces

    Science.gov (United States)

    Sinai, Ofer; Hofmann, Oliver T.; Rinke, Patrick; Scheffler, Matthias; Heimel, Georg; Kronik, Leeor

    2015-03-01

    The inclusion of the global effects of semiconductor doping poses a unique challenge for first-principles simulations, because the typically low concentration of dopants renders an explicit treatment intractable. Furthermore, the width of the space-charge region (SCR) at charged surfaces often exceeds realistic supercell dimensions. We present a multi-scale technique that addresses these difficulties. It is based on the introduction of excess charge, mimicking free charge carriers from the SCR, along with a fixed sheet of counter-charge mimicking the SCR-related field. Self-consistency is obtained by imposing charge conservation and Fermi level equilibration between the bulk, treated semi-classically, and the electronic states of the slab/surface, which are treated quantum-mechanically. The method, called CREST - the Charge-Reservoir Electrostatic Sheet Technique - can be used with standard electronic structure codes. We validate CREST using a simple tight-binding model, which allows for comparison of its results with calculations encompassing the full SCR explicitly. We then employ it with density functional theory, obtaining insight into the doping dependence of the electronic structures of the metallic clean-cleaved Si(111) surface and its semiconducting (2x1) reconstructions.

  6. Superhydrophobic and adhesive properties of surfaces: testing the quality by an elaborated scanning electron microscopy method.

    Science.gov (United States)

    Ensikat, Hans J; Mayser, Matthias; Barthlott, Wilhelm

    2012-10-09

    In contrast to advancements in the fabrication of new superhydrophobic materials, the characterization of their water repellency and quality is often coarse and unsatisfactory. In view of the problems and inaccuracies, particularly in the measurement of very high contact angles, we developed alternative methods for the characterization of superhydrophobic surfaces. It was found that adhering water remnants after immersion are a useful criterion in determining the repellency quality. In this study, we introduce microscopy methods to detect traces of water-resembling test liquids on superhydrophobic surfaces by scanning electron microscopy (SEM) or fluorescence light microscopy (FLM). Diverse plant surfaces and some artificial superhydrophobic samples were examined. Instead of pure water, we used aqueous solutions containing a detectable stain and glycerol in order to prevent immediate evaporation of the microdroplets. For the SEM examinations, aqueous solutions of lead acetate were used, which could be detected in a frozen state at -90 °C with high sensitivity using a backscattered electron detector. For fluorescence microscopy, aqueous solutions of auramine were used. On different species of superhydrophobic plants, varying patterns of remaining microdroplets were found on their leaves. On some species, drop remnants occurred only on surface defects such as damaged epicuticular waxes. On others, microdroplets regularly decorated the locations of increased adhesion, particularly on hierarchically structured surfaces. Furthermore, it is demonstrated that the method is suitable for testing the limits of repellency under harsh conditions, such as drop impact or long-enduring contact. The supplementation of the visualization method by the measurement of the pull-off force between a water drop and the sample allowed us to determine the adhesive properties of superhydrophobic surfaces quantitatively. The results were in good agreement with former studies of the water

  7. Investigations of the Electronic Properties and Surface Structures of Aluminium-Rich Quasicrystalline Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Jason A. Barrow

    2003-08-05

    equations. Transport behavior is described in terms of charge carriers and the mean-free time between carrier collisions. It is concluded that the mean-free time is much longer in the periodic direction than in the aperiodic direction. This difference produces the observed anisotropy in thermal transport. The third study presented a detailed analysis of the reversible, sputter-induced phase transformation which occurs on the 5-fold surface of an icosahedral Al-Cu-Fe quasicrystal. Reflection high-energy electron diffraction (RHEED), x-ray photoemission spectroscopy (XPS), and ultra-violet photoemission spectroscopy (UPS) data were collected as a function of annealing temperature and were used to probe surface structure, surface composition, and electronic structure, respectively. The composition and structure of the sputtered surface are consistent with a transformation to the {beta}-Al-Cu-Fe cubic structure, and shows a sharp metallic cut-off in the spectral intensity of the electronic structure at the Fermi edge. Upon annealing the surface reverts to a quasicrystalline composition and structure. This transformation has been correlated with a reduction in the spectral intensity of the electronic structure at the Fermi level. This data clearly demonstrates that the observed reduction is intrinsic to a quasicrystalline surface. It is concluded that this is due to the opening of a pseudo-gap in the electronic density of states as the surface reverts from {beta}-Al-Cu-Fe to quasicrystalline.

  8. Biomechanical and histological evaluation of roughened surface titanium screws fabricated by electron beam melting.

    Directory of Open Access Journals (Sweden)

    Jun Yang

    Full Text Available BACKGROUND: Various fabrication methods are used to improve the stability and osseointegration of screws within the host bone. The aim of this study was to investigate whether roughened surface titanium screws fabricated by electron beam melting can provide better stability and osseointegration as compared with smooth titanium screws in sheep cervical vertebrae. METHODS: Roughened surface titanium screws, fabricated by electron beam melting, and conventional smooth surface titanium screws were implanted into sheep for 6 or 12 weeks (groups A and B, respectively. Bone ingrowth and implant stability were assessed with three-dimensional imaging and reconstruction, as well as histological and biomechanical tests. RESULTS: No screws in either group showed signs of loosening. Fibrous tissue formation could be seen around the screws at 6 weeks, which was replaced with bone at 12 weeks. Bone volume/total volume, bone surface area/bone volume, and the trabecular number were significantly higher for a define region of interest surrounding the roughened screws than that surrounding the smooth screws at 12 weeks. Indeed, for roughened screws, trabecular number was significantly higher at 12 weeks than at 6 weeks. On mechanical testing, the maximum pullout strength was significantly higher at 12 weeks than at 6 weeks, as expected; however, no significant differences were found between smooth and roughened screws at either time point. The maximum torque to extract the roughened screws was higher than that required for the smooth screws. CONCLUSIONS: Electron beam melting is a simple and effective method for producing a roughened surface on titanium screws. After 12 weeks, roughened titanium screws demonstrated a high degree of osseointegration and increased torsional resistance to extraction over smooth titanium screws.

  9. Biomechanical and histological evaluation of roughened surface titanium screws fabricated by electron beam melting.

    Science.gov (United States)

    Yang, Jun; Cai, Hong; Lv, Jia; Zhang, Ke; Leng, Huijie; Wang, Zhiguo; Liu, Zhongjun

    2014-01-01

    Various fabrication methods are used to improve the stability and osseointegration of screws within the host bone. The aim of this study was to investigate whether roughened surface titanium screws fabricated by electron beam melting can provide better stability and osseointegration as compared with smooth titanium screws in sheep cervical vertebrae. Roughened surface titanium screws, fabricated by electron beam melting, and conventional smooth surface titanium screws were implanted into sheep for 6 or 12 weeks (groups A and B, respectively). Bone ingrowth and implant stability were assessed with three-dimensional imaging and reconstruction, as well as histological and biomechanical tests. No screws in either group showed signs of loosening. Fibrous tissue formation could be seen around the screws at 6 weeks, which was replaced with bone at 12 weeks. Bone volume/total volume, bone surface area/bone volume, and the trabecular number were significantly higher for a define region of interest surrounding the roughened screws than that surrounding the smooth screws at 12 weeks. Indeed, for roughened screws, trabecular number was significantly higher at 12 weeks than at 6 weeks. On mechanical testing, the maximum pullout strength was significantly higher at 12 weeks than at 6 weeks, as expected; however, no significant differences were found between smooth and roughened screws at either time point. The maximum torque to extract the roughened screws was higher than that required for the smooth screws. Electron beam melting is a simple and effective method for producing a roughened surface on titanium screws. After 12 weeks, roughened titanium screws demonstrated a high degree of osseointegration and increased torsional resistance to extraction over smooth titanium screws.

  10. Structural and electronic properties of low-index surfaces of NbAl3 intermetallic with first-principles calculations

    Science.gov (United States)

    Jiao, Zhen; Liu, Qi-Jun; Liu, Fu-Sheng; Tang, Bin

    2017-10-01

    The structural, electronic and surface properties of low-index surfaces of tetragonal NbAl3 have been studied with first-principles plane-wave ultrasoft pseudo-potential method based on density functional theory. The atomic relaxations, surface energies and work functions are reported. The calculated atomic relaxations and surface energies suggest that the (111) surface is the most stable stoichiometric surface. Furthermore, the Al-terminated (110) surface is thermodynamically stable than other surfaces in both Al-rich and Nb-rich conditions.

  11. First-principles study of electronic properties and stability of Nb5SiB2 (001) surface

    Institute of Scientific and Technical Information of China (English)

    Xu Yu-Jiang-Zi; Shang Jia-Xiang; Wang Fu-He

    2011-01-01

    The density functional calculations are performed to study the electronic structure and stability of Nb5SiB2 (001) surface with different terminations. The calculated cleavage energies along the (001) planes in Nb5SiB2 are 5.015 J ? m-2 and 6.593 J ? m-2 with the break of Nb-Si and Nb-NbB bonds, respectively. There exists a close correlation between the surface relaxation including surface ripple and the cleavage energy: the larger the cleavage energy, the larger the surface relaxation. Moreover, the surface stability of the Nb5SiB2 (001) with different terminations has been investigated by the chemical potential phase diagram. From a thermodynamics point of view, the four terminations can be stabilized under different conditions. In chemical potential space, NbB (Nb) and Nb (Si) terminations are just stable in a small area, whereas Si (Nb) and Nb (NbB) terminations are stable in a large area (the letters in brackets represent the subsurface atoms).

  12. Experimental Investigation of Space Radiation Processing in Lunar Soil Ilmenite: Combining Perspectives from Surface Science and Transmission Electron Microscopy

    Science.gov (United States)

    Christoffersen, R.; Keller, L. P.; Rahman, Z.; Baragiola, R.

    2010-01-01

    Energetic ions mostly from the solar wind play a major role in lunar space weathering because they contribute structural and chemical changes to the space-exposed surfaces of lunar regolith grains. In mature mare soils, ilmenite (FeTiO3) grains in the finest size fraction have been shown in transmission electron microscope (TEM) studies to exhibit key differences in their response to space radiation processing relative to silicates [1,2,3]. In ilmenite, solar ion radiation alters host grain outer margins to produce 10-100 nm thick layers that are microstructurally complex, but dominantly crystalline compared to the amorphous radiation-processed rims on silicates [1,2,3]. Spatially well-resolved analytical TEM measurements also show nm-scale compositional and chemical state changes in these layers [1,3]. These include shifts in Fe/Ti ratio from strong surface Fe-enrichment (Fe/Ti >> 1), to Fe depletion (Fe/Ti electron (FE-STEM) study of experimentally ion-irradiated ilmenite. A key feature of this work is the combination of analytical techniques sensitive to changes in the irradiated samples at depth scales going from the immediate surface (approx.5 nm; XPS), to deeper in the grain interior (5-100 nm; FE-STEM).

  13. Structural and electronic properties of ultrathin picene films on the Ag(100) surface

    Science.gov (United States)

    Kelly, Simon J.; Sorescu, Dan C.; Wang, Jun; Archer, Kaye A.; Jordan, Kenneth D.; Maksymovych, Petro

    2016-10-01

    Using scanning tunneling microscopy and electronic structure calculations, we investigated the assembly and electronic properties of picene molecules on the Ag(100), Ag(111), and Cu(111) surfaces, with particular emphasis on Ag(100). In each case, picene molecules are found to lie parallel to the surface at coverages up to half a monolayer and to adopt alternating parallel and tilted orientations at full monolayer coverage. In the latter case, the arrangement of the molecules is roughly similar to that in the bulk crystal. On the metal surfaces considered, the growth mode of picene is quite different from that of its structural isomer pentacene, which forms a bilayer overlayer on top of a dense monolayer of flat-lying molecules on metal surfaces. Tunneling spectroscopy measurements provide estimates of the energies of several low-lying unfilled molecular orbitals as well as of the highest occupied molecular orbital of the absorbed picene molecules. From analysis of these results, we establish that the on-site Coulomb repulsion for picene decreases by ~ 2 eV in going from the gas phase to the full monolayer on Ag(100), bringing it close to that of the undoped bulk crystal.

  14. The Fermi surface and f-valence electron count of UPt{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    McMullan, G J [MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 0QH (United Kingdom); Rourke, P M C; McCollam, A; Julian, S R [Department of Physics, University of Toronto, Toronto, ON, M5S 1A7 (Canada); Norman, M R [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Huxley, A D [School of Physics, James Clerk Maxwell Building, King' s Buildings, Mayfield Road, Edinburgh EH9 3JZ (United Kingdom); Doiron-Leyraud, N [Departement de Physique, Universite de Sherbrooke, Sherbrooke, PQ, J1K 2R1 (Canada); Flouquet, J [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA/Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9 (France); Lonzarich, G G [Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 OHE (United Kingdom)], E-mail: sjulian@physics.utoronto.ca

    2008-05-15

    Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt{sub 3}. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt{sub 3} are localized by correlation effects-agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt{sub 3}. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.

  15. The Fermi surface and f-valence electron count of UPt{sub 3}.

    Energy Technology Data Exchange (ETDEWEB)

    McMullan, G. J.; Rourke, P. M. C.; Norman, M. R.; Huxley, A. D.; Doiron-Layraud, N.; Flouquet, J.; Lonzarich, G. G.; McCollam, A.; Julian, S. R.; Materials Science Division; MRC Lab. Molecular Biology; Univ. of Toronto; School of Phys. Edinburgh; Univ. de Sherbrooke; CEA/Grenoble; Univ. of Cambridge

    2008-01-01

    Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt{sub 3}. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt{sub 3} are localized by correlation effects--agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt{sub 3}. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.

  16. A Portable Surface Contamination Monitor Based on the Principle of Optically Stimulated Electron Emission (OSEE)

    Science.gov (United States)

    Perey, D. F.

    1996-01-01

    Many industrial and aerospace processes involving the joining of materials, require sufficient surface cleanliness to insure proper bonding. Processes as diverse as painting, welding, or the soldering of electronic circuits will be compromised if prior inspection and removal of surface contaminants is inadequate. As process requirements become more stringent and the number of different materials and identified contaminants increases, various instruments and techniques have been developed for improved inspection. One such technique, based on the principle of Optically Stimulated Electron Emission (OSEE), has been explored for a number of years as a tool for surface contamination monitoring. Some of the benefits of OSEE are: it is non-contacting; requires little operator training; and has very high contamination sensitivity. This paper describes the development of a portable OSEE based surface contamination monitor. The instrument is suitable for both hand-held and robotic inspections with either manual or automated control of instrument operation. In addition, instrument output data is visually displayed to the operator and may be sent to an external computer for archiving or analysis.

  17. Electronic and Optical Properties of Aluminum Oxide Before and After Surface Reduction by Ar+ Bombardment

    Directory of Open Access Journals (Sweden)

    D. Tahir

    2014-08-01

    Full Text Available The electronic and optical properties of a-Al2O3 after induced by 3-keV Ar+ sputtering have been studied quantitatively by use of reflection electron energy loss spectroscopy (REELS spectra. The band gap values of a-Al2O3 was determined from the onset values of the energy loss spectrum to the background level of REELS spectra as a function of time Ar+ bombardment. The bandgap changes from 8.4 eV before sputtering to 6.2 eV after 4 minutes of sputtering.The optical properties of α-Al2O3 thin films have been determined by comparing the experimental cross section obtained from reflection electron energy loss spectroscopy with the theoretical inelastic scattering cross section, deduced from the simulated energy loss function (ELF by using QUEELS-ε(k-REELS software. The peak assignments are based on ELF and compared with reported data on the electronic structure of α-Al2O3 obtained using different techniques. The results demonstrate that the electronic and optical properties before and after surface reduction will provide further understanding in the fundamental properties of α-Al2O3 which will be useful in the design, modeling and analysis of devices applications performance.

  18. Surface modification of Al-Pb alloy by high current pulsed electron beam

    Institute of Scientific and Technical Information of China (English)

    LU You; LI Shi-long; AN Jian; LIU Yong-bing

    2006-01-01

    Al-Pb alloy was modified by high current pulsed electron beam and the microstructure, hardness and tribological characteristics were characterized by scanning electron microscopy, electronic microanalysis probe microanalysis, Knoop hardness indentation and pin-on-disc type wear testing machine. The results show that the microstructure and hardness can be greatly improved, and the modification layer consists of a molten zone, an overlapped zone of heat-affected and quasistatic thermal stress-affected zone and a transition zone followed by the substrate. The tribological properties of high current pulsed electron beam irradiated Al-Pb alloy are correspondingly improved largely. Optical observation and scanning electron microscopy analysis reveal that the low wear rate and lowest level in coefficient of friction at high load level for irradiated Al-Pb alloy are due to the formation of a lubricious tribolayer covering the worn surface, which is a mixture of Al2O3, Pb3O4 and silicate. The wear mode varies from oxidative wear at low load to film spalling at high load and, finally, adhesive wear.

  19. Space charge effect of the time-dependent ultrafast laser excited electron emission from a metal surface

    CERN Document Server

    Liu, Yangjie

    2013-01-01

    A model has been constructed to the study the transition of ultrafast laser excited electron emission from a metallic surface to the space charge limited (SCL) regime. By considering the time-dependent emission process by L. Wu et al. [Phys. Rev. B.78 224112 (2008)], we include the space charge effect which will affect the barrier at the emitting surface. At the high laser field, it is found that space charge effect cannot be ignored and the SCL current emission is reached. The threshold of the laser field to reach the SCL regime is determined. Our calculations agree well with particle-in-cell simulation results. This model is also compared with the classical short pulse SCL current model by A. Valfellset al. [Phys. Plasmas 9, 2377 (2002)].

  20. Observation and simulation of microdroplet shapes on surface-energy-patterned substrates: Contact line engineering for printed electronics

    Science.gov (United States)

    Noda, Yuki; Matsui, Hiroyuki; Minemawari, Hiromi; Yamada, Toshikazu; Hasegawa, Tatsuo

    2013-07-01

    Equilibrium microdroplet shapes on hydrophilic/hydrophobic patterned surfaces were investigated both by experimental observation using an inkjet printing technique and by computer simulation. We demonstrated that the hybrid energy minimization simulation can accurately reproduce the equilibrium shapes of observed microdroplets, including the droplet contact line in the vicinity of a sharp corner in the hydrophilic region. We found that the relative ratio of nonwetting areas by the droplets around a rectangular corner can be used as a useful index to check the reliability of the simulation as well as to estimate the surface-energy distribution within the hydrophilic region. Based on the estimation of the additional local force acting on the contact lines, we discuss the design rules for printed electronics circuits, such as the shapes of the integrated electrode to realize the ideal spreading.

  1. Demonstration of surface electron rejection with interleaved germanium detectors for dark matter searches

    Energy Technology Data Exchange (ETDEWEB)

    Agnese, R.; Balakishiyeva, D.; Saab, T.; Welliver, B. [Department of Physics, University of Florida, Gainesville, Florida 32611 (United States); Anderson, A. J.; Figueroa-Feliciano, E.; Hertel, S. A.; McCarthy, K. A. [Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Basu Thakur, R. [Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States); Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illnois 61801 (United States); Bauer, D. A.; Holmgren, D.; Hsu, L.; Loer, B.; Schmitt, R. [Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States); Borgland, A.; Brandt, D.; Brink, P. L.; Do Couto E Silva, E.; Godfrey, G. L.; Hasi, J. [SLAC National Accelerator Laboratory/Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Collaboration: The SuperCDMS Collaboration; and others

    2013-10-14

    The SuperCDMS experiment in the Soudan Underground Laboratory searches for dark matter with a 9-kg array of cryogenic germanium detectors. Symmetric sensors on opposite sides measure both charge and phonons from each particle interaction, providing excellent discrimination between electron and nuclear recoils, and between surface and interior events. Surface event rejection capabilities were tested with two {sup 210}Pb sources producing ∼130 beta decays/hr. In ∼800 live hours, no events leaked into the 8–115 keV signal region, giving upper limit leakage fraction 1.7 × 10{sup −5} at 90% C.L., corresponding to < 0.6 surface event background in the future 200-kg SuperCDMS SNOLAB experiment.

  2. Scanning electron microscopy of the tegumental surface of adult Schistosoma spindale.

    Science.gov (United States)

    Kruatrachue, M; Riengrojpitak, S; Upatham, E S; Sahaphong, S

    1983-09-01

    The tegumental surfaces of adult male and female of Schistosoma spindale were studied by scanning electron microscopy. In general, the body surface of the male appears to be fairly uniform from anterior end to posterior end. It is characterized by the presence of transverse ridges and papillae of various types. These papillae are distributed fairly regularly over the whole body surface of the worm. The tegument lining the gynecophoral canal of the male worm is covered with numerous spines interspersed with papillae, some without cilia and some with crater-like holes in the centres and apical cilia. The tegument of the female worm is covered with smooth and perforated ridges and sensory bulbs with apical nodules.

  3. Demonstration of Surface Electron Rejection with Interleaved Germanium Detectors for Dark Matter Searches

    Energy Technology Data Exchange (ETDEWEB)

    Agnese, R.; Anderson, A. J.; Balakishiyeva, D.; Basu Thakur, R.; Bauer, D. A.; Borgland, A.; Brandt, D.; Brink, P. L.; Bunker, R.; Cabrera, B.; Caldwell, D. O.; Cerdeno, D. G.; Chagani, H.; Cherry, M.; Cooley, J.; Cornell, B.; Crewdson, C. H.; Cushman, Priscilla B.; Daal, M.; Di Stefano, P. C.; Do Couto E Silva, E.; Doughty, T.; Esteban, L.; Fallows, S.; Figueroa-Feliciano, E.; Fox, J.; Fritts, M.; Godfrey, G. L.; Golwala, S. R.; Hall, Jeter C.; Harris, H. R.; Hasi, J.; Hertel, S. A.; Hines, B. A.; Hofer, T.; Holmgren, D.; Hsu, L.; Huber, M. E.; Jastram, A.; Kamaev, O.; Kara, B.; Kelsey, M. H.; Kenany, S.; Kennedy, A.; Kenney, C. J.; Kiveni, M.; Koch, K.; Loer, B.; Lopez Asamar, E.; Mahapatra, R.; Mandic, V.; Martinez, C.; McCarthy, K. A.; Mirabolfathi, N.; Moffatt, R. A.; Moore, D. C.; Nadeau, P.; Nelson, R. H.; Novak, L.; Page, K.; Partridge, R.; Pepin, M.; Phipps, A.; Prasad, K.; Pyle, M.; Qiu, H.; Radpour, R.; Rau, W.; Redl, P.; Reisetter, A.; Resch, R. W.; Ricci, Y.; Saab, T.; Sadoulet, B.; Sander, J.; Schmitt, R.; Schneck, K.; Schnee, Richard; Scorza, S.; Seitz, D.; Serfass, B.; Shank, B.; Speller, D.; Tomada, A.; Villano, A. N.; Welliver, B.; Wright, D. H.; Yellin, S.; Yen, J. J.; Young, B. A.; Zhang, J.

    2013-10-17

    The SuperCDMS experiment in the Soudan Underground Laboratory searches for dark matter with a 9-kg array of cryogenic germanium detectors. Symmetric sensors on opposite sides measure both charge and phonons from each particle interaction, providing excellent discrimination between electron and nuclear recoils, and between surface and interior events. Furthermore, surface event rejection capabilities were tested with two 210Pb sources producing ~130 beta decays/hr. We found that in ~800 live hours, no events leaked into the 8–115 keV signal region, giving upper limit leakage fraction 1.7 x 10-5 at 90% C.L., corresponding to<0.6 surface event background in the future 200-kg SuperCDMS SNOLAB experiment.

  4. Structure and electronic properties of graphene on ferroelectric LiNbO{sub 3} surface

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Jun, E-mail: dingjun@haue.edu.cn [College of Science, Henan University of Engineering, Zhengzhou 451191 (China); Wen, LiWei; Li, HaiDong [College of Science, Henan University of Engineering, Zhengzhou 451191 (China); Zhang, Ying, E-mail: yingzhang@bnu.edu.cn [Department of Physics, Beijing Normal University, Beijing 100875 (China)

    2017-05-25

    Highlights: • Interface structure of graphene on O terminated LiNbO{sub 3} surface. • Asymmetry gap around Dirac point. • Berry phase calculations confirm a valley Hall effect. - Abstract: We investigate the structural and electronic properties of graphene on the O terminated LiNbO{sub 3}(001) surface by density functional theory simulations. We observe that the first graphene layer is covalent bonded with the surface O atoms and buckles a lot. While considering second layer graphene upon the first layer, it almost recovers the planar structure and the interface interaction breaks the AB sublattice symmetry which leads to a valley Hall effect. Our results reveal the interface structure of graphene-ferroelectric heterostructure and provide the way for valleytronic applications with graphene.

  5. Distribution of surface glycoproteins on influenza A virus determined by electron cryotomography.

    Science.gov (United States)

    Wasilewski, Sebastian; Calder, Lesley J; Grant, Tim; Rosenthal, Peter B

    2012-12-07

    We use electron cryotomography to reconstruct virions of two influenza A H3N2 virus strains. The maps reveal the structure of the viral envelope containing hemagglutinin (HA) and neuraminidase (NA) glycoproteins and the virus interior containing a matrix layer and an assembly of ribonucleoprotein particles (RNPs) that package the genome. We build a structural model for the viral surface by locating copies of the X-ray structure of the HA ectodomain into density peaks on the virus surface. We calculate inter-glycoprotein distances and the fractional volume occupied by glycoproteins. The models suggest that for typical HA densities on virus, Fabs can bind to epitopes on the HA stem domain. The models also show how membrane curvature may influence the number of glycoproteins that can simultaneously interact with a target surface of receptors.

  6. Structural and electronic properties of bulk and low-index surfaces of zincblende PtC

    Science.gov (United States)

    Gokhan Sensoy, Mehmet; Toffoli, Daniele; Ustunel, Hande

    2017-03-01

    Transition metal carbides have been extensively used in diverse applications over the past decade. Their versatility is in part thanks to their unique bonding, which displays a mixture of ionic, metallic and covalent character. While the bulk structure of zincblende (ZB) PtC has been investigated several times, a detailed understanding of the electronic and structural properties of its low-index surfaces is lacking. In this work, we present an ab initio investigation of the properties of five crystallographic ZB PtC surfaces (Pt/C-terminated PtC(1 0 0), PtC(1 1 0) and Pt/C-terminated PtC(1 1 1)). Upon geometry optimization, both polar and nonpolar surfaces undergo a mild interlayer relaxation, without extensive reconstructions. Calculated vacancy formation energies indicate facile C removal on the (1 1 1) surface while Pt-vacancy formation is endothermic. Finally, atomic O adsorption energies on all surfaces reveal a high affinity of the C-terminated surfaces towards this species.

  7. Surface Electronic Structure of Hybrid Organo Lead Bromide Perovskite Single Crystals

    KAUST Repository

    Komesu, Takashi

    2016-08-24

    The electronic structure and band dispersion of methylammonium lead bromide, CH3NH3PbBr3, has been investigated through a combination of angle-resolved photoemission spectroscopy (ARPES) and inverse photoemission spectroscopy (IPES), as well as theoretical modeling based on density functional theory. The experimental band structures are consistent with the density functional calculations. The results demonstrate the presence of a dispersive valence band in MAPbBr3 that peaks at the M point of the surface Brillouin zone. The results also indicate that the surface termination of the CH3NH3PbBr3 is the methylammonium bromide (CH3NH3Br) layer. We find our results support models that predict a heavier hole effective mass in the region of -0.23 to -0.26 me, along the Γ (surface Brillouin center) to M point of the surface Brillouin zone. The surface appears to be n-type as a result of an excess of lead in the surface region. © 2016 American Chemical Society.

  8. Structural and electronic properties of bulk and low-index surfaces of zincblende PtC.

    Science.gov (United States)

    Sensoy, Mehmet Gokhan; Toffoli, Daniele; Ustunel, Hande

    2017-03-29

    Transition metal carbides have been extensively used in diverse applications over the past decade. Their versatility is in part thanks to their unique bonding, which displays a mixture of ionic, metallic and covalent character. While the bulk structure of zincblende (ZB) PtC has been investigated several times, a detailed understanding of the electronic and structural properties of its low-index surfaces is lacking. In this work, we present an ab initio investigation of the properties of five crystallographic ZB PtC surfaces (Pt/C-terminated PtC(1 0 0), PtC(1 1 0) and Pt/C-terminated PtC(1 1 1)). Upon geometry optimization, both polar and nonpolar surfaces undergo a mild interlayer relaxation, without extensive reconstructions. Calculated vacancy formation energies indicate facile C removal on the (1 1 1) surface while Pt-vacancy formation is endothermic. Finally, atomic O adsorption energies on all surfaces reveal a high affinity of the C-terminated surfaces towards this species.

  9. Surface characterization of ginger powder examined by X-ray photoelectron spectroscopy and scanning electron microscopy.

    Science.gov (United States)

    Zhao, Xiaoyan; Ao, Qiang; Du, Fangling; Zhu, Junqing; Liu, Jie

    2010-09-01

    The surface composition of five types of ginger powders with the particle sizes of 300, 149, 74, 37 and 8.34 microm was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and various types of physical-chemical characteristics regarding material particle size distributions, discoloration and chemical composition. The results show that the color differences are greater for superfine ground ginger than for conventional comminuted ones; the values of crude fibre, neutral detergent fiber (NDF) and acid detergent fiber (ADF) decrease with decreasing ginger particle size. However, no relationship with the surface fat, crude protein, ash and total solids exists. With superfine grinding the XPS O/C ratios of the five ginger powders were similar since the surfaces were not oxidized. Correlations were observed between the XPS N/C ratios and the high resolution XPS N 1s spectra. SEM observations revealed that the surface of ginger powder with a particle size of 300 microm is rougher, while superfine ground powders with particle sizes of 149, 74, 37 and 8.34 microm are similar to each other. This roughness difference between these surfaces correlates with the differences in their O/C ratios and the surface morphology of five ginger powders. Copyright 2010 Elsevier B.V. All rights reserved.

  10. Effect of Autoclave Cycles on Surface Characteristics of S-File Evaluated by Scanning Electron Microscopy.

    Science.gov (United States)

    Razavian, Hamid; Iranmanesh, Pedram; Mojtahedi, Hamid; Nazeri, Rahman

    2016-01-01

    Presence of surface defects in endodontic instruments can lead to unwanted complications such as instrument fracture and incomplete preparation of the canal. The current study was conducted to evaluate the effect of autoclave cycles on surface characteristics of S-File by scanning electron microscopy (SEM). In this experimental study, 17 brand new S-Files (#30) were used. The surface characteristics of the files were examined in four steps (without autoclave, 1 autoclave cycle, 5 autoclave cycles and 10 autoclave cycles) by SEM under 200× and 1000× magnifications. Data were analyzed using the SPSS software and the paired sample t-test, independent sample t-test and multifactorial repeated measures ANOVA. The level of significance was set at 0.05. New files had debris and pitting on their surfaces. When the autoclave cycles were increased, the mean of surface roughness also increased at both magnifications (Pautoclave increased the surface roughness of the files and this had was directly related to the number of autoclave cycles.

  11. Investigations on electronic, Fermi surface, Curie temperature and optical properties of Zr2CoAl

    Science.gov (United States)

    Wei, Xiao-Ping; Sun, Weiwei; Zhang, Ya-Ling; Sun, Xiao-Wei; Song, Ting; Wang, Ting; Zhang, Jia-Liang; Su, Hao; Deng, Jian-Bo; Zhu, Xing-Feng

    2017-03-01

    Using full-potential local-orbital minimum-basis along with spin-polarized relativistic Korringa-Kohn-Rostoker methods, we study the electronic, Fermi surface, Curie temperature and optical properties of Zr2CoAl alloy. The alloy with Li2AgSb and Cu2MnAl structures are compared in terms of magnetic properties, and the electronic structures in two structures are also discussed. According to the calculated electronic states, it finds that the Zr2CoAl with Li2AgSb structure is half-metallic ferromagnet with an integral magnetic moment of 2.00μB , meanwhile we also notice the d-d and p-d hybridizations are responsible for the formation of minority-spin gap, furthermore, the fat-bands are applied to discuss the mixture between d and p electrons in the vicinity of the Fermi level. The Fermi surfaces related to the valence bands are constructed, and it is found that the spin-up valence bands 26, 27 and 28 across the Fermi energy dominate the nature of electrons. By mapping the system onto a Heisenberg Hamiltonian, we obtain the exchange coupling parameters, and observe that the Zr(A)-Co(C) and Zr(A)-Zr(B) interactions provide a major contribution for exchange interactions. Based on the calculated exchange coupling parameters, the Curie temperature is estimated to be 287.86 K at equilibrium, and also the dependence of Curie temperature on lattice constant related to the tunable Curie temperature in Zr2CoAl alloy is studied. Finally, we report the optical properties of Zr2CoAl alloy, and present the photon energy dependence of the absorption, the optical conductivity and the loss function.

  12. Measurement of surface recombination velocity for silicon solar cells using a scanning electron microscope with pulsed beam

    Science.gov (United States)

    Daud, T.; Cheng, L. J.

    1981-01-01

    The role of surface recombination velocity in the design and fabrication of silicon solar cells is discussed. A scanning electron microscope with pulsed electron beam was used to measure this parameter of silicon surfaces. It is shown that the surface recombination velocity, s, increases by an order of magnitude when an etched surface degrades, probably as a result of environmental reaction. A textured front-surface-field cell with a high-low junction near the surface shows the effect of minority carrier reflection and an apparent reduction of s, whereas a tandem-junction cell shows an increasing s value. Electric fields at junction interfaces in front-surface-field and tandem-junction cells acting as minority carrier reflectors or sinks tend to alter the value of effective surface recombination velocity for different beam penetration depths. A range of values of s was calculated for different surfaces.

  13. Surface engineered two-dimensional and quasi-one-dimensional nanomaterials for electronic and optoelectronic devices

    Science.gov (United States)

    Du, Xiang

    As the sizes of individual components in electronic and optoelectronic devices approach nano scale, the performance of the devices is often determined by surface properties due to their large surface-to-volume ratio. Surface phenomena have become one of the cornerstones in nanoelectronic industry. For this reason, research on the surface functionalization has been tremendous amount of growth over the past decades, and promises to be an increasingly important field in the future. Surface functionalization, as an effective technique to modify the surface properties of a material through a physical or chemical approach, exhibits great potential to solve the problems and challenges, and modulate the performance of nanomaterials based functional devices. Surface functionalization drives the developments and applications of modern electronic and optoelectronic devices fabricated by nanomaterials. In this thesis, I demonstrate two surface functionalization approaches, namely, surface transfer doping and H2 annealing, to effectively solve the problems and significantly enhance the performance of 2D (single structure black phosphorus (BP) and heterostructure graphene/Si Schottky junction), and quasi-1D (molybdenum trioxide (MoO 3) nanobelt) nanomaterials based functional devices, respectively. In situ photoelectron spectroscopy (PES) measurements were also carried out to explore the interfacial charge transfer occurring at the interface between the nanostructures and doping layers, and the gap states in MoO 3 thin films, which provides the underlying mechanism to understand and support our device measurement results. In the first part of this thesis, I will discuss the first surface functionalization approach, namely, surface transfer doping, to effectively modulate the ambipolar characteristics of 2D few-layer BP flakes based FETs. The ambipolar characteristics of BP transistors were effectively modulated through in situ surface functionalization with cesium carbonate (Cs2

  14. Atomic Spectral Methods for Ab Initio Molecular Electronic Energy Surfaces: Transitioning From Small-Molecule to Biomolecular-Suitable Approaches.

    Science.gov (United States)

    Mills, Jeffrey D; Ben-Nun, Michal; Rollin, Kyle; Bromley, Michael W J; Li, Jiabo; Hinde, Robert J; Winstead, Carl L; Sheehy, Jeffrey A; Boatz, Jerry A; Langhoff, Peter W

    2016-08-25

    Continuing attention has addressed incorportation of the electronically dynamical attributes of biomolecules in the largely static first-generation molecular-mechanical force fields commonly employed in molecular-dynamics simulations. We describe here a universal quantum-mechanical approach to calculations of the electronic energy surfaces of both small molecules and large aggregates on a common basis which can include such electronic attributes, and which also seems well-suited to adaptation in ab initio molecular-dynamics applications. In contrast to the more familiar orbital-product-based methodologies employed in traditional small-molecule computational quantum chemistry, the present approach is based on an "ex-post-facto" method in which Hamiltonian matrices are evaluated prior to wave function antisymmetrization, implemented here in the support of a Hilbert space of orthonormal products of many-electron atomic spectral eigenstates familiar from the van der Waals theory of long-range interactions. The general theory in its various forms incorporates the early semiempirical atoms- and diatomics-in-molecules approaches of Moffitt, Ellison, Tully, Kuntz, and others in a comprehensive mathematical setting, and generalizes the developments of Eisenschitz, London, Claverie, and others addressing electron permutation symmetry adaptation issues, completing these early attempts to treat van der Waals and chemical forces on a common basis. Exact expressions are obtained for molecular Hamiltonian matrices and for associated energy eigenvalues as sums of separate atomic and interaction-energy terms, similar in this respect to the forms of classical force fields. The latter representation is seen to also provide a long-missing general definition of the energies of individual atoms and of their interactions within molecules and matter free from subjective additional constraints. A computer code suite is described for calculations of the many-electron atomic eigenspectra and

  15. Facet-dependent trapping and dynamics of excess electrons at anatase TiO2 surfaces and aqueous interfaces

    Science.gov (United States)

    Selcuk, Sencer; Selloni, Annabella

    2016-10-01

    Excess electrons from intrinsic defects, dopants and photoexcitation play a key role in many of the properties of TiO2. Understanding their behaviour is important for improving the performance of TiO2 in energy-related applications. We focus on anatase, the TiO2 polymorph most relevant in photocatalysis and solar energy conversion. Using first-principles simulations, we investigate the states and dynamics of excess electrons from different donors near the most common anatase (101) and (001) surfaces and aqueous interfaces. We find that the behaviour of excess electrons depends strongly on the exposed anatase surface, the environment and the character of the electron donor. Whereas no electron trapping is observed on the (101) surface in vacuo, an excess electron at the aqueous (101) interface can trigger water dissociation and become trapped into a stable surface Ti3+-bridging OH complex. By contrast, electrons avoid the (001) surface, indicating that oxidation reactions are favoured on this surface. Our results provide a bridge between surface science experiments and observations of crystal-face-dependent photocatalysis on anatase, and support the idea that optimization of the ratio between {101} and {001} facets could provide a way to enhance the photocatalytic activity of this material.

  16. Surface and Bulk Electronic Structure and Chemisorption Properties of Titanium and Vanadium Oxides

    Science.gov (United States)

    Smith, Kevin Eugene

    The unusual electronic properties of Ti _2O_3 and V _2O_3, in particular the metal-insulator transitions which they undergo, have produced widespread interest in the physics of these materials, while the use of titanium and vanadium oxides as catalysts and catalyst supports makes a detailed understanding of their surface properties of great importance. The electronic structure and gas adsorption properties of single crystal titanium and vanadium oxides have been studied here using ultraviolet and x-ray photoemission spectroscopy, synchrotron radiation, Auger electron spectroscopy and low energy electron diffraction. Spatially anisotropic resonant photoemission from 3d states in Ti_2O_3 and V_2O_3 was observed and shown to originate from localised molecular orbitals. This contrasts with an energy analysis of the photoemission data which revealed dispersing, delocalised d-bands in both oxides. A large resonance was observed in the O 2p emission at the cation 3p to 3d absorption edge in Ti_2O _3 which is inconsistent with hybridisation, indicating the possible existence of inter-atomic resonances. The first detailed photoemission observation of metal-insulator transitions in Cr-doped V_2O _3 is reported; large changes in the density of states at the Fermi level are seen at these transitions. The surface electronic structure of single crystal TiO_2, Ti_2O _3 and V_2O _3 was found to be indistinguishable from that of the bulk. The interaction of SO_2 with these oxides was extensively studied since sulfur is a notorious catalyst poison. SO_2 reacts vigorously with the titanium oxides, dissociating in the presence of Ti^{3+} cations to form TiO_2 and TiS _2; in their absence no reaction occurs. Surprisingly, SO_2 reacts very weakly with V _2O_3, adsorbing in both dissociated and molecular form. Additionally, only a weak reaction of H_2S and TiO _2 was found. The electronic structure of these oxides is shown to be extremely complex, displaying both localised and

  17. Cytochrome C on a gold surface: investigating structural relaxations and their role in protein-surface electron transfer by molecular dynamics simulations.

    Science.gov (United States)

    Siwko, Magdalena E; Corni, Stefano

    2013-04-28

    Proteins immobilized on inorganic surfaces are important in technological fields such as biosensors, enzymatic biofuel cells and biomolecular electronics. In these frameworks, it has been demonstrated that some proteins are able to keep their functionality, although the latter may be somewhat modified by the interaction with the surface. Cytochrome C, an heme-based electron transfer protein, has been found to be able to exchange electrons with the gold surface on which it is immobilized, but some deviations from the expected electron transfer rates were evidenced [C. A. Bortolotti, et al., J. Phys. Chem. C 2007, 111, 12100-12105]. In this work we have used molecular dynamics simulations of (native and mutated) yeast cytochrome C supported on Au(111) to investigate the microscopic picture behind the experimental behavior of the molecule. In particular, we have focused on the structural re-arrangements due to the interactions with the surface. We found that, despite being secondary-structure preserving, they can profoundly affect protein-surface electronic coupling and, in turn, electron transfer rates, explaining experimental findings. The conformational flexibility of the protein in the region of the protein-surface bond is thus pivotal in determining the resulting ET functionality of the immobilized protein.

  18. Imaging surface acoustic wave dynamics in semiconducting polymers by scanning ultrafast electron microscopy.

    Science.gov (United States)

    Najafi, Ebrahim; Liao, Bolin; Scarborough, Timothy; Zewail, Ahmed

    2017-08-24

    Understanding the mechanical properties of organic semiconductors is essential to their electronic and photovoltaic applications. Despite a large volume of research directed toward elucidating the chemical, physical and electronic properties of these materials, little attention has been directed toward understanding their thermo-mechanical behavior. Here, we report the ultrafast imaging of surface acoustic waves (SAWs) on the surface of the Poly(3-hexylthiophene-2,5-diyl) (P3HT) thin film at the picosecond and nanosecond timescales. We then use these images to measure the propagation velocity of SAWs, which we then employ to determine the Young's modulus of P3HT. We further validate our experimental observation by performing a semi-empirical transient thermoelastic finite element analysis. Our findings demonstrate the potential of ultrafast electron microscopy to not only probe charge carrier dynamics in materials as previously reported, but also to measure their mechanical properties with great accuracy. This is particularly important when in situ characterization of stiffness for thin devices and nanomaterials is required. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. Comparing Multiple Evapotranspiration-calculating Methods, Including Eddy Covariance and Surface Renewal, Using Empirical Measurements from Alfalfa Fields in the Sacramento-San Joaquin River Delta

    Science.gov (United States)

    Clay, J.; Kent, E. R.; Leinfelder-Miles, M.; Lambert, J. J.; Little, C.; Paw U, K. T.; Snyder, R. L.

    2016-12-01

    Eddy covariance and surface renewal measurements were used to estimate evapotranspiration (ET) over a variety of crop fields in the Sacramento-San Joaquin River Delta during the 2016 growing season. However, comparing and evaluating multiple measurement systems and methods for determining ET was focused upon at a single alfalfa site. The eddy covariance systems included two systems for direct measurement of latent heat flux: one using a separate sonic anemometer and an open path infrared gas analyzer and another using a combined system (Campbell Scientific IRGASON). For these methods, eddy covariance was used with measurements from the Campbell Scientific CSAT3, the LI-COR 7500a, the Campbell Scientific IRGASON, and an additional R.M. Young sonic anemometer. In addition to those direct measures, the surface renewal approach included several energy balance residual methods in which net radiation, ground heat flux, and sensible heat flux (H) were measured. H was measured using several systems and different methods, including using multiple fast-response thermocouple measurements and using the temperatures measured by the sonic anemometers. The energy available for ET was then calculated as the residual of the surface energy balance equation. Differences in ET values were analyzed between the eddy covariance and surface renewal methods, using the IRGASON-derived values of ET as the standard for accuracy.

  20. Effect of Surface Hydrogen Coverage on Field Emission Properties of DiamondFilms Investigated by High-Resolution Electron Energy Loss Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    WANG Yu-Guang; XIONG Yan-Yun; LIN Zhang-Da; FENG Ke-An; GU Chang-Zhi; JIN Zeng-Sun

    2000-01-01

    The influence of surface hydrogen coverage on the electron field emission of diamond films was investigated by high-resolution electron energy loss spectroscopy. It was found that hydrogen plasma treatment increased the surface hydrogen coverage while annealing caused hydrogen desorption and induced surface reconstruction. Field electron emission measurements manifested that increase of surface hydrogen coverage could improve the field emission properties, due to the decrease of electron affinity of the diamond .surface hy hvdrogen adsorption.